Fix conversations

[connyduck]

This fixes several problems with conversations (the code is basically just taken over from the newer timeline code)

• timestamps now update on pull-to-refresh
• the view now jumps up a bit to reveal newly loaded items after pull-to-refresh
• "nothing here" shown when conversations are empty instead of nothing
• when replying from conversations, the "replying to" field will be correctly filled
• the "fabHide" setting is now respected in the ConversationsFragment as well
• and most importantly, pagination now works as expected

kind of a prerequisite to #2552

I'd like to merge this at the same time as #2549 because the migrations overlap

[connyduck]

draft because some details still aren't perfect

[connyduck]

While this is a hundred times better than before, there are still 2 glitches:

• When the database is empty and conversations load for the first time, the list does not start at the top and one has to scroll up. I think is because of the load state footer that is shown and the recyclerview trying to keep the position. No idea how to turn this behavior off, I tried a lot.
• When having a long list of conversations and being way down, suddenly jumping up shows the wrong views for a split second. This is because paging from database does not hold all data in memory. We have the same behavior in timelines.

[charlag]

I'm a not so confident with all the paging APIs but maybe it's worth leaving a comment on how/why order works? I don't understand it fully, does server not reorder them all the time?

[connyduck]

I'm a not so confident with all the paging APIs but maybe it's worth leaving a comment on how/why order works? I don't understand it fully, does server not reorder them all the time?

Yes it does reorder it all the time but I also reload it all the time. After a pull to refresh there is only the current page in the cache.