Merge pull request #136 from babs/code-refactoring-trans-fr

Code refactoring French translation.
Fixed "invalid constraint name" error on domain editing form. (issue
ModelWidget class refactoring done.
Class FormPrincipal renamed to MainWindow.
MainWindow class refactoring checkpoint. Pending comment translation.
pt_BR comment removed from config files.
Code refactoring process done.

Fixed bug related to the issue #139

Fixed bug related to the issue #138
Updated fr_FR :)