Security - disable conduit act as user by default

Summary: Introduce a new configuration setting that by default disables the conduit as as user method. Wordily explain that turning it on is not recommended. Fixes T3818.

Test Plan:
```
15:25:19 ~/Dropbox/code/phalanx/src/applications/conduit (T3818)
~>  echo '{}' | arc call-conduit --conduit-uri http://phalanx.dev/ user.whoami
Waiting for JSON parameters on stdin...
{"error":null,"errorMessage":null,"response":{"phid":"PHID-USER-tghb3b2gbdyezdcuw2or","userName":"btrahan","realName":"Bob Trahan","image":"http:\/\/phalanx.dev\/file\/data\/yncjbh7phk7ktrdhuorn\/PHID-FILE-qyf4ui3x2ll3e52hpg5e\/profile-profile-gravatar","uri":"http:\/\/phalanx.dev\/p\/btrahan\/","roles":["admin","verified","approved","activated"]}}
15:25:34 ~/Dropbox/code/phalanx/src/applications/conduit (T3818)

<go edit libconfig/conduitclient to spoof another user...>

~>  echo '{}' | arc call-conduit --conduit-uri http://phalanx.dev/ user.whoami
Waiting for JSON parameters on stdin...
{"error":"ERR-CONDUIT-CORE","errorMessage":"ERR-CONDUIT-CORE: security.allow-conduit-act-as-user is disabled","response":null}
15:26:40 ~/Dropbox/code/phalanx/src/applications/conduit (T3818)

<enable option via bin/config....>

~>  echo '{}' | arc call-conduit --conduit-uri http://phalanx.dev/ user.whoami
Waiting for JSON parameters on stdin...
{"error":null,"errorMessage":null,"response":{"phid":"PHID-USER-6lcglnzbkiamdofishgi","userName":"xerxes","realName":"Xerxes Trahan","image":"http:\/\/phalanx.dev\/file\/data\/n2kyeevowetcuynbcxrg\/PHID-FILE-voquikectzpde256zzvm\/profile-1275455993.jpg","uri":"http:\/\/phalanx.dev\/p\/xerxes\/","roles":["verified","approved","activated"]}}
```

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: jevripio, sowedance, epriestley, Korvin

Maniphest Tasks: T3818

Differential Revision: https://secure.phabricator.com/D9881
Modernize "repositories" typeahead datasource

Summary:
Ref T4420.

  - Allow tokenizers to accept either a `Datasource` object (new style) or a URI (old style).
  - Read URI and placeholder text from object, if available.
  - Swap the "repositories" datasource (which seemed like the simplest one) over to the new stuff.
  - Tweak/update the repo tokens a little bit.

Test Plan:
  - Used tokenizer in Herald, Differential (search), Differential (edit), Push Logs.
  - Grepped for other callsites.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4420

Differential Revision: https://secure.phabricator.com/D9874
Modernize "macro" typeahead datasource

Summary: Ref T4420. Make this modern.

Test Plan:
  - Used typeahead in remarkup comment area to select macro "derpdog".

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4420

Differential Revision: https://secure.phabricator.com/D9875
Modernize "legalpad" typeahead datasource

Summary: Ref T4420. Modernize legalpad.

Test Plan:
  - Used typeahead in Herald rules.
  - Used typeahead in Policy dialog.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4420

Differential Revision: https://secure.phabricator.com/D9876
Modernize "task priority" datasource

Summary: Ref T4420.

Test Plan:
  - Used typeahead in Herald rules.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4420

Differential Revision: https://secure.phabricator.com/D9877
Modernize "build plans" typeahead datasource

Summary: Ref T4420. Modernize build plans.

Test Plan:
  - Used build plan typeahead in Harbormaster.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4420

Differential Revision: https://secure.phabricator.com/D9878
Modernize "arcanist project" datasource

Summary: Ref T4420. Do arc projects.

Test Plan:
  - Used Herald typeahead.
  - Used Repositories typehaead.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4420

Differential Revision: https://secure.phabricator.com/D9879
Modernize "owners" datasource

Summary: Ref T4420. Update owners.

Test Plan:
  - Used typeahead from Herald.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4420

Differential Revision: https://secure.phabricator.com/D9880
Maniphest - add 'upforgrabs' hint in bulk editor

Summary: change typeahead placeholder to include 'or "upforgrabs" to unassign...' Fixes T2267. Well, makes it as good as its going to be until we get some new space age UI.

Test Plan: new text looks okay-ish

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T2267

Differential Revision: https://secure.phabricator.com/D9882
Modernize "projects" typeahead datasource

Summary: Ref T4420. Update "projects" source.

Test Plan:
- Edited projects on a Differential revision.
- Edited projects on a commit.
- Edited projects on a repository.
- Edited projects in feed search.
- Edited projects in a Herald rule field.
- Edited projects in a Herald rule action.
- Edited projects in Maniphest batch editor.
- Edited projects on Maniphest task.
- Edited projects in "Associate Projects..." action in Maniphest.
- Edited projects on Maniphest search in "all projects", "any project" and "not projects" fields.
- Edited projects on a Paste.
- Edited projects on a Pholio mock.
- Edited projects on a custom policy rule.
- Edited projects on a Ponder question.
- Edited projects on a Diffusion search query.
- Edited projects on a global search query.
- Edited projects on a slowvote.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4420

Differential Revision: https://secure.phabricator.com/D9884
Make it possible to configure Elasticsearch index name

Summary:
Similar to storage.default-namespace sometimes during development you'll want
to handle multiple indexes alongside one another. Rather than hardcoding the
/phabricator/ index make this exposed in new search.elastic.index setting,
defaulting to the existing "phabricator"

Test Plan:
Existing installations should be unaffected by this change. Changing the new
setting will result in new indexes being created when someone runs
`./bin/search index` again

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: 20after4, rush898, epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9798
Allow worker tasks to have priorities

Summary: Fixes T5336. Currently, `PhabricatorWorkerLeaseQuery` is basically FIFO. It makes more sense for the queue to be a priority-queue, and to assign higher priorities to alerts (email and SMS).

Test Plan: Created dummy tasks in the queue (with different priorities). Verified that the priority field was set correctly in the DB and that the priority was shown on the `/daemon/` page. Started a `PhabricatorTaskmasterDaemon` and verified that the higher priority tasks were executed before lower priority tasks.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Maniphest Tasks: T5336

Differential Revision: https://secure.phabricator.com/D9871
Merge branch 'upstream/master'