add unit tests for draft 3 'required' objects
fix failing 'required' testcase
refactor conditional logic of 'required' validation
types of draft 3 'required' properties are not checked when given as objects, add resp. unit tests
separate 'type' from 'required' validation, fixing failing unit tests
fix code style
Merge pull request #53 from alexmmm/fix-required-validation

Fix draft 3 'required' validation issues