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
Merge remote-tracking branch 'upstream/develop' into develop
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
Merge remote-tracking branch 'upstream/develop' into develop

Conflicts:
	src/main/scala/at/logic/skeptik/algorithm/compressor/package.scala
Remove reference fixedPremise, merge with main repository
Implement BWSm and rename old BWS to BWSt
Add let expression in VeriT format

Fix issue #68
Use bottomUp traversal in check of ancestor in the BWSm algorithm
Merge remote-tracking branch 'upstream/develop' into develop
Merge remote-tracking branch 'afellner/develop' into correction2
Add existsAmongAncestors method to ProofNode
Improve existsAmongAncestors for speed
Merge remote-tracking branch 'existsAA/feature/existsAA' into develop
Implement suggested changes in BWSt
Fix name method
Improve toString method