Basics of notifications
Reading notifications working client side
Likes for source sheets
--amend
Consolidate all DB connections across files
Only show likes on public sheets
Basic user to user messaging
Merge branch 'master' into messages

Conflicts:
	sefaria/urls.py
Login prompt for messaging
Event tracking for sheet likes and messages
Handle non post requests to notifications read api
Email unread notifications
Generate notifcations emails from separate templates
Functions for counting characters in a text
Merge branch 'notifications'
Don't return full text after successful text post
Allow fix case for completely erasing a text section from editor