Implemented a first version of the naive subsumption algorithm

I also created a test proof which shows the desired behaviour.
Relates to Issue #63
Implement suggested changes and add ForwardSubsumption to CLI
Make axioms subsumable and replace name ForwardSubsumption by FWS
Implement first version of RecycleUnits
Implement second version of RecycleUnits and a test for this algorithm.
Add RecycleUnits to CLI.
Implement BackwardSubsumption and intermediate RecyclePivot algorithms

Add both to CLI and include testcases for BackwardSubsumption
Remove reference fixedPremise, merge with main repository
Implement BWSm and rename old BWS to BWSt
Use bottomUp traversal in check of ancestor in the BWSm algorithm
Add existsAmongAncestors method to ProofNode
Improve existsAmongAncestors for speed