core: Add a 'super' property to inheriting classes

* Fix typo in example where it said ".prop" (doesn't exist)
  instead of ".static".
* Show usage example for the new super property.
* Add unit tests for super.
* Improve existing unit tests to test that instance properties
  added by the constructor are being set as expected.

Change-Id: Ic301140d2e0ad99eddc83f9031e12a7641fd10ae