Added header to feed list.

A header has been added to the beginning of the feed list which shows
the subreddit and page number. Eventually this header will be added to
every "page" or every 25 items, and the page label on the header will
increment.
Added scroll to settings view, put padding around login label, and made
it multiline.
Added 'to top' and 'to bottom' and 'refresh' actions to feed view.
Comments list now only shows the author in the subtitle. Used to be
"Submitted by {author} to {subreddit}.
Upvote and downvote context actions will only work if user is logged in.
If not, displays toast telling them to login.