R1:b072e937b5fc

Modernize blog UI

Summary:
Cleans up some of the mess I made in D3694. Basically:

- All blogs have an "internal" view with posts that uses mobile-friendly UIs, etc., so we don't have to do as much work with skins -- they just have to look pretty.
- Blogs now have a separate "live" view that we use to handle domains / skins.
- Simplified some views and use IDs in some URLs for consistency.
- Delete a bunch of edge/blogger/multi-blog code that's now obsolete.

Test Plan: Will attach screenshots.