Add Dario's GSOC code (temporal reasoning in PLN)
Remove obsolete python stuff
Remove an obsolete hack from the PLN test examples
Get rid of FWVariableNodes from python PLN code
Revert "Add support for a list of allowed rules. And start figuring out how to add forward chaining into the backward chainer."

This reverts commit cbdb436e6e614010790be5d4a99ba76115a94afb.
Integrating temporal formulas code
Chainer can handle temporal rules, but the formula gives a probability of -4.3 (???)