- conclusions do not reference Contexts anymore; 
- separated (read-only) methods in Contexts used for rule applications
to ContextPremises; 
- added hybrid contexts that are now used in ContextCompleteionFactory
Merge branch 'feature/rules-refactoring' of
https://github.com/klinovp/elk.git into feature/rules-refactoring

Conflicts:
	elk-reasoner/src/main/java/org/semanticweb/elk/reasoner/saturation/rules/DummyRuleVisitor.java
	elk-reasoner/src/main/java/org/semanticweb/elk/reasoner/saturation/rules/LinkRule.java