T2385: Add "Delete Document" action to Phriction pages

Summary: If a page has not been deleted, this adds an action button to delete the document in the menu on the Phriction Page.

Test Plan:
1. Created a document, checked whether "Delete Document" button was visible.
2. Clicked on "Delete Document" button, checked that the document had been deleted.
3. Went back to document page, checked that the "Delete Document" button no longer existed.

Reviewers: epriestley

CC: aran, Korvin

Maniphest Tasks: T2385

Differential Revision: https://secure.phabricator.com/D4636