Phriction - policy front end changes

Summary:
Ref T4029. Fixes T6034.

Various front-end miscellania here. See D10814#96251. This more or less makes policy work but I am not going to call it "fixed" here since we need D10814 to be deployed too and will do that manually.

Test Plan:

• changed document policy from web ui and changes persisted
• changed document policy from web and had form error and changes persisted
• created a structure like users/users/justmyuserpolicy and made sure another user could delete the users/users/ doc
• moved a doc from a to b and verified policy persisted
• verified stub documents inherited policy of the document that stub them...!
• uploaded a file and verified that it 1) had the permissions of the page it was added to and 2) had an "attached" tab linking back to the page on the file page (this means T6034 is fixed with this)

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6034, T4029

Differential Revision: https://secure.phabricator.com/D10816