Add 'repr' method

A shortcut method that gets the Representation of
a model and initializes it with the model.
add grading assignment objects,methods,specs
Merge branch 'master' of github.com:canadaduane/openagent into grading
added grading category spec for events builder
Move repr to SIF.repr
Add message.datatype
added SIF.repr to spec
Merge branch 'master' of github.com:canadaduane/openagent