Define bulk edits in terms of EditEngine, not hard-coded ad-hoc definitions

Summary:
Depends on D18862. See PHI173. Ref T13025. Fixes T10005. This redefines bulk edits in terms of EditEngine fields, rather than hard-coding the whole thing.

Only text fields -- and, specifically, only the "Title" field -- are supported after this change. Followup changes will add more bulk edit parameter types and broader field support.

However, the title field now works without any Maniphest-specific code, outside of the small amount of binding code in the ManiphestBulkEditor subclass.

Test Plan: Used the bulk edit workflow to change the titles of tasks.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13025, T10005

Differential Revision: https://secure.phabricator.com/D18863