Allow Herald's "Reviewers" field to select project reviewers

Summary: The "Reviewers" condition in Differential Revision rules has the wrong typeahead and can't select projects, but should be able to.

Test Plan: {F79273}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D7526
Support ecdsa-sha2-nistp256 SSH keys

Summary:
See discussion in <https://github.com/facebook/phabricator/issues/430>.

(If we end up with more than like 5 of these we should probably make this a warning or something instead, the only goal is to prevent user error.)

Test Plan:
{F79196}

{F79197}

Reviewers: btrahan, chad

Reviewed By: chad

CC: aran, enko

Differential Revision: https://secure.phabricator.com/D7522
Phriction - make the check for project sub pages more fine-grained

Summary:
we were just checking if projects/ was in the URI before barfing. Use some more fun utility functions such that we only complain if there is no project.

Fixes T4071.

Test Plan: made a subpage under a project - success! tried to make a project wiki page where there was no project - successful failure! tried to make a project wiki sub page where there was no project - successful failure!

Reviewers: epriestley, chad

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T4071

Differential Revision: https://secure.phabricator.com/D7527