edje: Hide edje_global from the rest of the world
Call provider_find on the loop (or basically any object) with the
color/text/size class interface instead, to find it. The main loop is
the main holder of those objects.
Note: This makes use of provider_find instead of direct access to the
variable, in order to self-test the code. In theory release builds will
not do this and user directly the variable.