Change groupList() and name() to use the groupnames only, not the full path.
This is a first step towards hiding the separator used for nested groups in the ini backend. Full solution needs to wait for 4.1

Along the way add notes to the API's that can create groups that the forward slash "/" is not allowed as part of the group name.

Add tests for all the above.

Patch ok'ed on kde-core-devel.