Initial commit for data comparison condition and associated test

I've added a @todo for getContextDefinitions()
I would like to see protected helper methods for every operator. e.g. $this->isEqual() / $this->isGreaterThan(), etc. That way we can easily test them separately in our unit tests (to be added).

I would also suggest you move the "case '==':" and "default:" to the bottom. Makes it more readable (might just be me though).