Fix is_date_field for simple types

Having a simple type returned from e.g. a hybrid_property, an
`AttributeError` would be thrown from `is_date_field`. Fixed by checking
for the `property` attribute before accessing it. Added test case that
provoked the error prior to the fix.
Merge branch 'logandk/hybrid_setter_error' into master-patched
Fix tests for feature manually specify model relation endpoints.
Fixed doc string, has_field should work for hybrid_propery fields as far as I can tell.
Allow filtering of exposed model relation endpoints.
Merge branch 'master-define-relation-endpoints' into master-patched