Copy text/Delete single message/time stamp options

Added ability to long press single messages, and copy text or delete a
single message (this menu can open options for forwarding messages as well, if that's something anyone is interested in).

Also added new preferences for time stamps, so users can use 12-hr/24-hr,
as well as display full time stamps (including the date) if they wish.

I'm open to implementing even more options for time stamps, if there's a need. I know the design principles are to keep things simple, but forcing a 24-hour time stamp doesn't seem fair.