Render deleted files in Phragment as disabled

Summary: This updates Phragment so that fragments that are currently considered deleted have a disabled status and have an additional attribute 'Deleted'.  It also places this effect on versions (in the history controller) that actually involve deleting the file.

Test Plan: Viewed deleted fragments and versions.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T4205

Differential Revision: https://secure.phabricator.com/D7737