Migrate to python3 style for raise and import

This is the first step to migrate to python 3 2 fixes from futurize have been applied : fix_raise and fix_absolute_import A coding style test has been added to prevent regression : ERP5Python3CodingStyleTestSuite, a test suite is running with it There were very few string exceptions which had to be migrated to exception class And only 2 import paths had to be updated to import from Products...