Added clonePrefixed method, used by next developments
Added derivedIndexes to BP::Model::Concept and several additional classes, in order to get all the BP::Model::Index instances related to that concept
MongoDB now creates all the declared indexes on the collections where the concept instances are going to be stored
Now prefixed indexes keep it separated from the attribute names, so the different BP::Loader::Mapper implementations can decided what to do
Updated metadata index generation, and index prefix handling