R1:0e07ef8d560c

Mostly modernize post edit/detail UIs

Summary:
Still some big chunks left but this moves us a bit closer to getting everything device-ready.

Stuff not addressed here but which I'm planning to do soon:

- Posts don't have a live URI yet.
- Post detail pages don't actually show the post content. I'm going to tweak PhabricatorObjectPropertyListView for this since we need it some other places.
- Some of the hinting about use/states is gone (e.g., "This post is a draft, publish it to make it live to the…