Add a Delete link to Differential inline comment previews

Summary:
This lets you delete inlines from the preview at the bottom of
the page, instead of hunting for them through the diffs.

There is not yet a keyboard shortcut.

The mechanism for updating the inlines in the diffs is kind of a hack
and I'm sure I'm special-casing way too much, but at least it works.

Test Plan:
Load revision with many diffs. Create inlines all over the
place. Delete them all. Mwahaha.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T1433, T1431

Differential Revision: https://secure.phabricator.com/D3131