[FIX] website_mail: fixed is_follower controller, that could leak data about records.
Added instead a controller to get alias data. This controller is called by the
discussion group snippet to have the info about the alias.
[FIX] website_mail, websit_mail_group: moved discussion group snippet to the right module; it should not be available when the mailing list archives module is not installed. Also fixed get_alias_info route to be mail_group specific and to avoid allowing people to browse the database.
Merge pull request #251 from odoo-dev/saas-4-follower-route-tde

[FIX] website_mail_group: discussion group snippet
- moved into website_mail_group, instead of having the snippet in website_mail and the archives in website_mail_group
- fixed routes to avoid security issues
- better display of email on groups and archive