tests: Move test_gi.TestPropertiesObject into test_properties

Move all property testing code into the test_properties module.

https://bugzilla.gnome.org/show_bug.cgi?id=726999
tests: Break TestPropertiesObject up for re-use

Refactor TestPropertiesObject into a base class which abstracts get/set
property methods. This will allow re-use for testing both get/set_property()
and the props accessor.

https://bugzilla.gnome.org/show_bug.cgi?id=726999
tests: Add tests for get/set_property()

Re-use the new CPropertiesTestBase class for testing get/set_property()
methods.

https://bugzilla.gnome.org/show_bug.cgi?id=726999
tests: Move test_everything.TestProperties into test_properties

Consolidate property tests found in test_everything into test_property
removing redundant tests already found in test_property.

https://bugzilla.gnome.org/show_bug.cgi?id=726999
tests: Move object property reference count tests to test_properties

Move and consolidate tests for object property reference counts from
tests_object_marshaling to test_properties.

https://bugzilla.gnome.org/show_bug.cgi?id=726999