Make "Assign / Claim" stacked action work properly in Maniphest

Summary:
Ref T9132. This is kind of a mess because the tokenizer rewrite left rendering tokenizers in Javascript a little rough. This causes bugs like icons not showing up on tokens in the "Policy" dialog, which there's a task for somewhere I think.

I think I've fixed it enough that the beahavior is now correct (i.e., icons show up properly), but some of the code is a bit iffy. I'll eventually clean this up properly, but it's fairly well contained for now.

Test Plan:

• Reassigned a task.
• Put a task up for grabs.
• No reassign on closed tasks.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9132

Differential Revision: https://secure.phabricator.com/D14669