Show user availability dots (red = away, orange = busy) in typeaheads, tokenizer tokens, and autocompletes

Summary:
Ref T13249. See PHI810. We currently show availability dots in some interfaces (timeline, mentions) but not others (typeheads/tokenizers).

They're potentially quite useful in tokenizers, e.g. when assigning tasks to someone or requesting reviews. Show them in more places.

(The actual rendering here isn't terribly clean, and it would be great to try to unify all these various behaviors some day.)

Test Plan:

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13249

Differential Revision: https://secure.phabricator.com/D20173