Bug #41266 rename group fails if the new name differs only in case from existing name

Description:
The "rename goup" function fails with

   U0105 This group name is already in use. Enter a different name.

if the new group name is different to the existing one only in the used case.

How to repeat:
- create a group "MERLIN"
- create try to rename it to "Merlin"

work around:
rename in 2 steps (first add any char, then change to the wanted new name)

the UI was prechecking for group existence, but did not consider
group names case in a case insensitive manner.

tests were added at the UI, business, and persistence layers to
ensure we could rename groups to a different case.

committed to trunk.  awaiting review for push into 2.0 GA or 2.0.1 maintenance.

pushed to 2.0 maintenance branch, awaiting build.

tested OK in 2.0.2.7126

An entry was added to the 2.0 changelog:

The Rename Group function failed if the new group name was different to the current one only in the case used; for example, if “Merlin” was changed to “MERLIN”.

The error generated was:

U0105 This group name is already in use. Enter a different name.