Heuristic added that greatly improves performance.

On the first pass through the theorems, only bound theorem expressions
that have at least one symbol in the goal (or a goal subexpression) are
inserted into the VC.

Also added a time to quit parameter to the applyTo method in the Theorem
class.
Removed java 8 dependencies.

Now compliant with java 7.
Merge pull request #121 from mikekab/TheoremBridging

Heuristic added that greatly improves performance.