Fix for last unread for some users

That didn't work at all. If someone read a mixtape but you did not, it
wouldn't show up on your list. This is a messy solution in a messy
codebase for a messy application. It's also really fucking late.
Use state to hide notifications on back button

It checks the href (latest unread) and as long as it matches what is in
the state, it hides it since you've seen it.
Add comment validator
Comment feed