User Groups corrections: Should have an edit action in context menu, Dialog should be more usable

Go to User Groups menu and double click on one of groups. You'll see a dialog for editing the group properties. This dialog should be shown not on double click, but it rather should be present in context menu. The context menu is already there, but we need to add an item 'Edit Group' there with respective action.
Additionally - Enter and Esc buttons should work for the dialog.