Replace thread posts goto views with redirect views that use new generics and permissions system

[rafalp]

All goto views tests are currently failing, but its okay because those are simple to rewrite for new permissions and generics system.

Requires new read tracker to be completed first (#1618).

Also should include new ThreadRepliesPaginator because we are dropping "repeat last post from previous page on the start of next page" thing. But we will need to know whats the first post on next page to pull thread events to display below the last post. The "which page the post is on" logic should actually live in a method on this new paginator class.

We should also have a generic redirect to post by its ID view that will be able to redirect to either private thread or regular thread. That will simplify the "go to the quoted post" logic.