initial commit for a mixed module store which can interoperate with both XML and Mongo module stores
add a set_modulestore_configuration to the modulestore interface. This can be used to pass in settings run the Django tier
WIP: added a get_modulestore_type. Added some unit tests. changed over the isinstance() with respect to modulestores to use this get_modulestore_type()
remove unneeded type check on the modulestore
WIP
fix tests
remove debugging logging
remove another debug logging message
update file comment on MixedModuleStore