Added MutableFactoryTest.testAddingClassSimpleAPIwithJMX() to test that the statistics are still collected after the method addClasses(Class<?>... classes) invocation, verifying that the total number of queries (searchQueryCount) and the size of the set of the indexed classes (indexedClasses) are both updated in the right way.
The JMX console and the statistics generation are both activated.

SearchFactoryTest added the method Statistics getStatistics() to this interface
ImmutableSearchFactory added the code to handle the copy of the previous statistics. The field isStatisticsEnabled is setted only in case of new creation.
MutableSearchFactoryState added the copy of the statistics and the getter and setter for the Statistics object itself