Improve wrapping and overflow behavior for curtain panels containing long usernames

Summary:
Ref T13486. When a curtain element like "Author" in Maniphest has a very long username, the wrapping and overflow behavior is poor: the date is obscured.

Adjust curtain elements which contain lists of references to other objects to improve wrapping behavior (put the date on a separate line) and overflow behavior (so we get a "..." when a name overflows).

Test Plan:

Maniphest Tasks: T13486

Differential Revision: https://secure.phabricator.com/D20966