User-controlled sorting of room list

[neilalexander]

The rooms list is not sorted. It would be good to have some options in the user settings about this, i.e. sort by message most recently received, sort alphabetically, sort manually (by dragging and dropping), sort channels with unread messages at the top, etc.

[neilalexander]

Room sorting logic is implemented now, although the lists aren't configurable by settings yet. Going to remove this from the v0.1 milestone as it's probably not urgent to implement that straight away.

[aaronraimist]

Pinning of rooms would be great