Made ScriptedEffect throw an exception if bad

If an invalid effect class is specified this will throw an exception so
you can fallback to something else.
Item rendering cleanup
Changed service located to return weak ptrs

Lets keep ownership under control, OK?
Follow up for weak_ptr usage
Fixed origin parsing for item templates
Added "defaults" function to script environment

Utility function for ensuring default values are there.
Added support for config values to scripted items
Merge pull request #46 from zackthehuman/master

Item template parsing, other random changes