Add option to select which toolbar is "simple" in the Global Profile

Right now it is possible to change it by changing CKEDITOR_FORCE_SIMPLE_TOOLBAR_NAME constant.
This constant shouldn't be removed, because it is possible to delete the global profile, so if the global profile does not exist CKEDITOR_FORCE_SIMPLE_TOOLBAR_NAME will be used like before.
However, if the global profile exists, we should take the name of simple toolbar from it.