Filter messages by unread

[SQL-MisterMagoo]

Add a button to only show unread messages

[SQL-MisterMagoo]

this is done, I'll just wait for Mark's PR to go through before I PR this as it does contain a tiny little bit of scss.

[SQL-MisterMagoo]

I've decided to hold off on this one as it's not that useful and to make it useful needs more work.

Currently, I was just filtering the list by unread, but that doesn't magically go back and fetch unread older messages.

There is an API call to get a list of unread messages, but if the list is long we will very quickly hit the API rate limit trying to fetch them individually.

So, what we probably want to do it get the list of unread, then start fetching messages from the oldest using the normal routine - but filtering along the way. This is unlikely to hit the rate limit but will probably be slower (maybe?) and will use more bandwidth. So it might be something we need to restrict on mobile (although as an option/setting because I know I wouldn't care about the bandwidth).