R1:3f11c8a602f0

Tweak Maniphest CSS, fix remarkup in description change views

Summary:
Various CSS tweaks and fixes:

- Add remarkup styling to description change views, missed this before.
- Fix CSS so that transactions with only one item (e.g., changed priority)
don't have weird floater underneath them.
- Add more space between transaction items.
- Make default background color lighter and less heavy.
- Use beigey color for comment form in Maniphest.
- Share more CSS between Maniphest and Differential…