Groups variable in base grouped mapper

To simplify the code around the group name, this PR moves the groups variable out of the admin class and into the BaseGroupedMapper class. 
This means that the access to the array is more controlled and will hopefully avoid issues with trying to keep the version in the mapper and the admin class in sync. 
To allow the existing code to work on the groups, the value of the groups array is copied to the admin class groups variable after the mapper has been built. 
Some of the group related code on the admin class has been deprecated by this PR, and these methods will not work anymore. These methods have been marked as such.