Clean up Maniphest Batch Editor UI
Summary: Finishes up work on PHUIInsetForm, cleans up the UI a bit when editing multiple tasks
Test Plan:
Edit multiple tasks, apply some new projects, still works as expected.
{F236044}
Reviewers: btrahan, epriestley
Reviewed By: epriestley
Subscribers: Korvin, epriestley
Differential Revision: https://secure.phabricator.com/D10881