radical change of locking for insert/delete/search/serialization in the voronoi tree; it's faster now

moving all answers to a different package; changing hierarchy of operations and answers; answer 'ProcessObjectsAnswer' now contains 'skipped_objects' field with reasons to skip the objects

bucket dispatcher moved from VoronoiTreeIndex to MIndex; renamed mindex.algorithms.* to mindex.algorithm.*

 * added a method to calculate object count according to allObjects iterations on leaf nodes

 * version 2.8.6 - requires MESSIF version 2.1.9

    - and thus the settings parameter "ppcalculator.threads" is supported no more
 * other minor modifications in the PPP-Tree (necessary for PPP-COdes)

 * many things modified :-)

 * added the concept of duplicate DC filter that is usable especially in the memory version of multi-overlay M-Index
    - there is some commented code to be removed later

 * fixed returning of supproted operations

 * parallel & sequential MIndexInitalizer merged into a single class
These two modifications caused changes in most of the files 

 * javadoc modifications

 * fixed a bug in MultiBucket split in MIndexLeafCell (caused when the index is built by massive multi-threading)
 * updates in M-Index property generation