Maniphest Tasks + Project Boards - some polish

Summary:
Fixes T4550 by changing supportsFeed to shouldPublishFeedStory, so things can be more granular like that are with mail. Attempts to fix things generally too, filtering out xactions that have no business in feed, etc.

Also return an updated Task HTML representation on drag and drop moves, etc. This is important so if the priority changes you can see it reflected in the UI.

Test Plan: dragged tasks around. observed no feed stories on subpriority drags. observed feed stories and updated color bars on stories that changed priority

Reviewers: epriestley, chad

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T4550

Differential Revision: https://secure.phabricator.com/D8399