[FEATURE] Notification settings for each group member

[shurwit]

Is your feature request related to a problem? Please describe.
Currently users can set notification settings that configure what notifications they receive from all groups. We want to be able to let the user select what notifications they want to receive for each individual group.

Describe the solution you'd like
We should include a new settings field in the group membership model where users can specify which notifications they want to receive for a given group.