Allow users to follow others

[ceolinwill]

Is your feature request related to a problem? Please describe.
It's hard to know when a user posts something new.

Describe the solution you'd like
A new feature that allows users to follow others.

Describe alternatives you've considered
N/A.

Additional context
This ticket should implement the following functionalities:

• When a user posts something, adds the post to their followers' timeline
• When a user unfollows another user, remove their posts from the timeline
• Send a notification when a user starts following you
• Add a link to view the user profile on the notification
• Add a follow/unfollow button to the profile page
• Add followers list to user profile
• Followers list is private (not visible to other users)
• Add following list to user profile
• Following list is private (not visible to other users)
• Display a following/followers count