adds a new function and shortcut to cycle unread chats in reverse order

[desgua]

This adds a new shortcut (by default control + u) to cycle thorgh unread chats from the oldest unreaded to the newer.

[d99kris]

Thanks for contributing, will take a look and see how/if it fits the ui. An immediate concern is that delete_line_before_cursor is already mapped to KEY_CTRLU, but we could of course find some other (available) key binding.

[d99kris]

Note to self: This is addressing feature request #359

[desgua]

Thank you so much for checking this specifically and for the amazing software that nchat is. I'm sorry I didn't see KEY_CTRLU was already in use.

[desgua]

If you want I can carefully check which shortcut is avaliable and make another commit.

[d99kris]

If you want I can carefully check which shortcut is avaliable and make another commit.

Thanks for offering but It's not needed, let me review the PR first (hopefully this weekend or next). Later I can always adjust the shortcut when integrating the PR.