Use PHUIListItemView in ConpherenceThreadList

Summary: Fixes T12556 Uses more common components in ConpherenceThreadList by moving to PHUIListItemView. Reduces clutter by moving privacy into the header. Gets ride of "See More" double interchanges.

Test Plan:
I need to test this more, doesn't seem to auto-select top room any more, also might build a lipsum generator.

• Create lots of rooms with various policies
• Test clicking on policy object
• Click on different rooms
• Post in rooms
• Load up second account, see room numbers
• Clear room message count by clicking on room

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T12556

Differential Revision: https://secure.phabricator.com/D17698