Made shared clear spec a bit better
Add remove_child method to slot to avoid demeter violation
well images do not even understand clear
Fix a bug where slot would try to call gui#clear upon removal resulting in nomethoderror
Convert last direct instance variable usages with method access instead
Use non clever test set up with a class that includes the method
Use Class.new instead of polluting the name space
#clear -> #remove on the backend for non collections
Merge pull request #746 from shoes/fix-common-remove

Fix common remove to allow removal of slots

* Changelog: bugfix
* also go from #clear --> #remove on the backend