xAPI validator: Split base methods to base class.
xAPI validator: Move more helper methods to base class.
xAPI validator: Move more helper methods to base class. (continue)
xAPI validator: Cleanup validation methods.
xAPI validator: Fix wrong method name calling.
xAPI validator: Add todo item.
xAPI validator: Rename getStarted to validateStructure.
xAPI validator: Clean up validateStructure() method.
xAPI validator: Add new method -- fillMissingElements().
Merge branch 'work/andy' of code.adurolms.com:adurolms/lrs into work/andy

* 'work/andy' of code.adurolms.com:adurolms/lrs:
  xAPI validator: Clean up validateStructure() method.
xAPI validator: Clean up validateObject().
xAPI validator: Make object validation logic to a separated class.
xAPI validator: Move context validation logic to new class.
xAPI validator: Move result validation logic to new class.
xAPI validator: Make checkTypes() readable.
xAPI validator: Format more code.
xAPI validator: Fix typo.
xAPI validator: Adding statement fixture.
xAPI validator: Adding more statement fixtures.
xAPI validator: Adding more statement fixtures (continue).