R1:386dcfff7ed1

Rough batch editor for Maniphest

Summary:
First stab at a batch editor for Maniphest. Basically, you can select a group of
tasks and then import them into the "batch" interface, where you can edit all of
them at once.

High level goal is to make it easier for users in PM/filer/support/QA roles to
deal with large numbers of tasks quickly.

This implementation has a few major limitations:

- The only available actions are "add projects" and "remove projects".
- There is no review / undo / log stuff.