R1:fc9db6e2a2ee

Put subprojects and milestones back into the Project UI

Summary: Ref T10010. Restores subprojects and milestones to the UI with a more modern style and more warnings.

Test Plan:
{F1085207}

{F1085208}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10010

Differential Revision: https://secure.phabricator.com/D15152