Category instances for group, add_group, comm_group, and add_comm_group.

We introduce the bundled categories:

Group
AddGroup
CommGroup
AddCommGroup along with the relevant forgetful functors between them, and to the bundled monoid categories.

Implementation notes

See the note [locally reducible category instances].

The category of groups and group morphisms.

Construct a bundled Group from the underlying type and typeclass.

The category of commutative groups and group morphisms.

Construct a bundled CommGroup from the underlying type and typeclass.