Group map files

The group map controls how groups are created at startup.  This is used by the
UI to save groups from one execution to the next.  It's very very basic - each
line is one of the following formats:

GROUP: <TAG> <Name>
LINK: <BSSID> <TAG>

Tags take the form of BSSIDs (XX:XX:XX:XX:XX:XX) and must be unique.