Use CmsObjectCollection in listInTheme

This will implement the CmsObjectCollection for the listInTheme call. This alows the usage of the ->sort() method for page. 

Also this was a question as to the usage of the CmsObjectCollection at large. I see it in CmsObjectQuery but no where else, instead arrays are being passed around. Is this just not completely implemented yet or is there something else going on here?

Also included are updated unit tests.