Must enable blocking users

[bobness]

• [x] Add buttons on AuthorViewScreen and NewsViewScreen below Follow/Unfollow
• [x] Add new pg table to link users' blocking
• [x] Add new route to POST new block
• [x] Edit route(s) to not show this user
  • [x] HomeScreen::unread_summaries
  • [x] summaries::via id -- 404 on their summaries, and don't show their comments