Fixed typo.
Added owner to initial fake sim entry.
Use hasattr rather than try/except.

Changed
-------
* Use 'if hasattr' rather than a try/except because the try/except was
  masking other AttributeErrors.
Create sims with current user as the owner.
Added link_objects and href properties to Sim.
Added assertions for resources and collections.

Added
-----
* New validator classes to validate collections and resources. These
  classes are meant to be subclassed for specific resources.
Added test_sims.py for testing sims entry point.