A closed commit can be reopened, if allowed by the config file.
Summary: Fixes T2316
Test Plan:
When the config file allows reopening,
navigate to a closed revision and reopen it in the user interface,
and verify that the revision now "needs review."
Also checks that the reopen option is unavailable when disallowed
by the config file.
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin
Maniphest Tasks: T2316
Differential Revision: https://secure.phabricator.com/D4526