[Feature Request]: Follow Users

[NA0341]

Problem

Currently there's only the ability to add packets to your own lists ~ but there isn't a way to follow users and optionally get notified about configurable actions they do.

Solutions

Add support for following Users on ContentDB.

Including:

• Ability to subscribe to the users different activity feeds (new package, package change, comment, review, etc)
• Option to only have the user in your "following" list without getting any notifications.
• Followers & Following count on User Profiles.

[rubenwardy]

related #291