Improved the ontologic reasonner

The get_missig_taxonomy_stmts method was not complete, a lot of possible
deductions was neglected because 1) dynamic onto classes was not updated inside
recursives iterations 2) it didn't return new equivalent classes

Added tests (test_reason.py) to bring out the importance of this improvement
[tests] Clean-up + properly split tests into 'base' and 'reasonner'
[reasonner] Code refactoring + doc!