Blender Git Loki

Fix T51680: 'Delete Group' from Group view of Outliner does not work.

Do not call invoke ops from outliner's operations menus. Invoke op would
search again for item under mouse coordinates... when it is invoked!
Means often entry menu you would have clicked would not be over target
item, leading to either nothing or operation being applied to wrong item.

Note: about groups, there is another minor annoyance leading to some
assert - groups have an annoying virtual fake user which breaks
usercount, will see whether this is easily fixable. :|