Test performance will now hold the base class for performance tests as
well as tests related to the ORM, depending only on base. A new module
test_mail is introduced at this commit that contains performance tests
related to mail module. This commit contains only code move and should
not impact anything.
Future commits will move mail tests into test_mail so that all mail
related tests are located in the same optional module. This allows
notably to avoid creating a lot of unnecessary tables when installing
mail module on production databases.
Thibault Delavallée