Support bulk edit of "points" for Maniphest tasks

Summary: Ref T13025. Fixes T10973. Fairly straightforward. The "points" type is just an alias for "text" today.

Test Plan: Bulk edited points.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13025, T10973

Differential Revision: https://secure.phabricator.com/D18889