Code refactoring: 'loadConcepts' method has been renamed to 'mapData'
With no input files, model-mapper.pl generates the native models.
Code cleanup
Global variable controlling whether to generate code for abstract concepts is now parameterized.
Two variables used in one packages were moved to the other one
Dead code was breaking the run
New mapper: documentation generator

All the code in model-doc-generator.pl has been transferred and
adapted to the BP::Loader::Mapper's model, so model-mapper.pl can
generate documentation with a proper project file.
Path handling fixes on BP::Loader::Mapper::DocumentationGenerator
model-doc-generator.pl now calls BP::Loader::Mapper::DocumentationGenerator

As all the code has been properly transferred from model-doc-generator.pl
to BP::Loader::Mapper::DocumentationGenerator, it does not make sense to
keep code duplication.

This utility is going to be deprecated, in favour of model-mapper.pl