[BUG] Group Transformation Class uses "name" as input

[jmumford]

Generally, "name" is used to refer to the transformation identity. As shown in munge.py.

This means "name" cannot be used as a parameter within any transformation, but it is used here in the Group transformation class.

Proposed fix (Jeanette will do this when she has time): replace 'group' with 'group_name' in the Group class definition.