Make oracles easier to create by adding helper functions

This is going to be a series of commits to address https://github.com/IainNZ/JuMPeR.jl/issues/26
At the same time I'm going to be moving to a better, more functional style to improve code quality.

The first commit adds a new function that takes an uncertain constraint and makes it certain. It was extract from the polynomial oracle, and is written so that it is stateless and can be (and is)  tested - the actual task of adding the constraint still falls to the oracle, but I think thats for the best as it might want to do something with it anyway. It has been used in both bertsim and polyhedral, deleted 83 lines and added 70, which given tests were added is a Good Thing.

@vgupta1 if you feel brave, it'd be good to checkout this branch to make sure nothing goes wrong, although I'm 99% sure it won't since it is so self-contained.