Restarting Entity to fit in with new ES.
tests for back references
renaming of entity namespace.

removing old version files
renamed Entity to Model, as the Entity class is
going to be used for something else.
This existing system will remain alongside the new
Entity/Component/System architecture.
Further renaming of entity to model.

first set of tests for components.
testing creating with initial attributes
converted most component registry calls to callbacks.
Further adjustments
wrapping json-schema functions in a specific module.
added middleware type hooks for entity registry so
that sync modules can be used for data persistence.
clarified entity functions
hooks for component middleware. don't like the
middleware term...
retrieval of properties from a schema