Added a proper abstract constructor to BP::Loader::Mapper
Method mapData has been generalized and migrated from BP::Loader::Mapper::MongoDB to BP::Loader::Mapper
Added more type checks and setFilePrefix method to BP::Loader::Mapper
Constructors of BP::Loader::Mapper::* now call superclass constructor before
reading the configuration file
Replaced JSON::true and JSON::false by boolean::true and boolean::false