Add bookmarks and favorites timeline pages

This MR does not add bookmarking functionality (that will appear in another patch, since that's more involved) but does add the favorites and bookmarks pages:

(Yes I realize that it adds another border-style icon, so the drawer looks even more inconsistent...)

I was going to create a whole new model for these, but I realized that they function exactly the same as regular timelines (public, federated, etc) so I reused that class :-) I added a few clauses for the different API urls.