Make yellow "draft" bubbles more generic

Summary:
Fixes T12095. Ref T6660. The old code for this was specific to Differential, using the DifferentialDraft table.

Instead, make the EditEngine / VersionedDraft code create and remove a <objectPHID, authorPHID> edge when a particular author creates drafts.

Some applications have drafts beyond VersionedDrafts, notably inline comments. Before writing "yes, draft" or "no, no draft", ask the object if it has any custom draft stuff we need to know about.

This should fix all the yellow bubble bugs I created in T11114 and allow us to bring the feature to Audit fairly easily.

Test Plan: Created and deleted comments and inlines, reloading the list view after each change. Couldn't find a way to break the list view anymore.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12095, T6660

Differential Revision: https://secure.phabricator.com/D17205