PURPOSE
Mass mailing is currently a bit messy. As SMS will be added as a way to notify
people in mass through SMS let us take this opportunity to somehow clean this
application: organization, light code cleaning, model renaming.
SPECIFICATIONS
Rename mail.mass_mailing.stage and mail.mass_mailing.tag models to mailing.
stage and mailing.tag. Rationale :
* mailing is now a prefix for models in mass mailing;
* mailing.stage and mailing.tag are easier to read / find / understand;
MIGRATION
mail.mass_mailing.stage model -> mailing.stage
mail_mass_mailing_stage table -> mailing_stage
mail.mass_mailing.tag model -> mailing.tag
mail_mass_mailing_tag table -> tag
LINKS
Task ID 2037906
Preparing task ID 1997464 (SMS addition in mass mailing)
PR #34938