[ADD] add argument no_version for migrate decorator to force loading ...

In version 8.0, during a migration, if a new module has to be installed (due to new dependency for instance), pre- and post- migration files are not loaded anymore. 

It can be usefull to pass sometimes in those files, for instance to not create a new ir_model_data that have been move to the new module (that will be installed).

This pull request revert this change (so pre- and post- migration files will be taken into account as before v 8.0) and adds a new argument 'no_version' in the decorator 'migrate'.
If no_version is True, it will pass threw the method wrap in the decorator. By default it's False to keep the "official" behaviour.