OAuth - add a little notes section for admins to remember details about external accounts

Summary: Fixes T4755. This also includes putting in a note that Google might ToS you to use the Google+ API. Lots of code here as there was some repeated stuff between OAuth1 and OAuth2 so I made a base OAuth with less-base OAuth1 and OAuth2 inheriting from it. The JIRA provider remains an independent mess and didn't get the notes field thing.

Test Plan: looked at providers and read pretty instructions.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T4755

Differential Revision: https://secure.phabricator.com/D8726
Add a priorityColor property to the maniphest conduit endpoint

Summary:
I added a getTaskPriorityColor function to the ManiphestTaskPriority class which returns the color set in the maniphest config for the given priority.

This is in preparation for a change to arcanist which will allow it to display the priority color (if it is a supported color) upon running `arc tasks`.

Fixed some linting issues

Test Plan:
Invoke the maniphest.info method from conduit and ensure that:
 * The priorityColor property is given in the json
 * the priorityColor property is set correctly

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D8734
Disable rate limiting by default in general

Summary: This is still too rough to enable by default. We can turn it on for `secure.phabricator.com` and tweak it a bit first, and then release it in general with higher defaults and more sensible behavior in edge cases.

Test Plan: Loaded some pages.

Reviewers: btrahan, spicyj

Reviewed By: spicyj

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D8736
Merge branch 'master' of http://github.com/facebook/phabricator