Add support for defining group types

Add a field to Group defining a type for that group, as a foreign key to a GroupType that can be dynamically managed.

changed milestone to %2.0a2

added part::backend type::feature workflow::discussing labels

created merge request !213 (merged) to address this issue

mentioned in merge request !213 (merged)

added workflow::confirmed label and removed workflow::discussing label

closed via merge request !213 (merged)

mentioned in commit 108cf780