Some BibClassify improvements (see details).

• I wrote coherent outputs for bibclassify in 3 verbose levels (errors, warnings and info). For this, bibclassify_utils was added. It contains the write_message method that originates from bibtask.
• I changed the imports and content from bibclassify_cli. Now the latter only imports methods from bibclassifylib which takes the role of the main method of bibclassify.
• I created bibclassify_ontology_handler which contains all methods related to the management of the cache and the creation of the regular expressions.