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.
Test the new lower-in-the-middle rule for RedRec (WIP)
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
Merge remote-tracking branch 'origin/feature/lowerMiddle' into lowerMiddle
Curryfy RedRec functions
Simplify RedRec.reduce
Fix lowerMiddle rule
Use bottomUp traversal in check of ancestor in the BWSm algorithm
Merge remote-tracking branch 'upstream/develop' into develop
Prepare code for tests
Merge remote-tracking branch 'afellner/develop' into correction2
Add existsAmongAncestors method to ProofNode