Make Maniphest Transaction preview tokenizer aware

Summary:
...pretty sure the JS is too hack-tastic but it works...! :D

also fixed a small error from assert_instances_of change where a null value is all errors and what have you

Test Plan: played around with tasks in firefox and safari. made cc, owner, and project changes, as well as priority, etc.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran

Maniphest Tasks: T1074

Differential Revision: https://secure.phabricator.com/D2234