Added groupings to the boards menu

I got so fed up with how big the boards menu is, and the fact that I can't get at many of the entries in it on my computer (Linux, AwesomeWM), that I implemented groupings (sub-menus) in the boards menu.

There is now a new "xxx.group=Group Name" entry in the boards.txt files.  A submenu is made for each of these groups named "Group Name", and all boards with that same "Group Name" are placed within it.

If no group is specified the board remains in the top level boards menu.

Groups have been added to all existing boards in both pic32 and Arduino.