Add granularity to notifications

Is your feature request related to a problem? Please describe.

Admins and users can receive a lot of unwanted notifications, but can't be precise about what they want or do not want to receive. If they think they receive too much notifications, their only option is to disable completly the mails in notifications settings.

But sometimes, a user following a participatory space juste want to receive a notification when a new proposal is made, not for each comment posted.

Describe the solution you'd like

As a user, I'd like to be able to select the type of contents submited to notifications, in my notifications settings.

Describe alternatives you've considered

None.

Does this issue could impact on users private data? Ex. issues related with user's sign up/sign in process, verifications, invitations, sensitive data like email, IP addresses, etc.

No.