worker local todo: new methods to check if the local queue is activated
(should be used) and deactivating; checking that all methods are called
from the same thread
fixed a bug when inserting initialization into a context: a context was
marked unsaturated after the insertion which (incorrectly) could result
in a worker seeing a context as initialized and saturated
setting saturation of context is now synchronized to avoid inconsistency
and duplicates in nonSaturatedContexts queue of the SaturationState
Improved stability & correctness of ClassExpressionSaturationFactory.
Reduced the number of counters. Moved some counters to SaturationState.
No longer needs to use a listener to track modified contexts.
simplified rule application factories
fixed statistics (was not averaging times); introduced
AbstractStatistics for the common code
Merge branch 'master' into feature/tracing-new

Conflicts:
	elk-reasoner/src/main/java/org/semanticweb/elk/reasoner/saturation/ClassExpressionSaturationFactory.java
	elk-reasoner/src/main/java/org/semanticweb/elk/reasoner/saturation/rules/factories/AbstractRuleApplicationFactory.java
	elk-reasoner/src/main/java/org/semanticweb/elk/reasoner/saturation/rules/factories/RuleApplicationAdditionPruningFactory.java
interpreting local rules as rules which produce conclusions which belong
to the current context (current w.r.t the conclusion being processed) or
any of its subcontexts.
moving the tracing-related benchmarking updates from the old branch
genericizing SaturationState so that one can type-safely get extensions
of Context when using specific implementations of the interface