Merge pull request #1558 from jetaggart/master

Change all paths to be relative to root
Implement notifications page
Delete notification app
Delete backbone
Add task to create alerts about notifications
Update about page
Merge branch 'notifications'
Duplicate layout in haml in main app

This will allow us to start porting templates to haml one at a time.
Do not try to show notifications to guests
Move help back into main app
Add getting started page in main app
Simplify homepage
Delete leftover notification javascript
Delete more left-over notification stuff
Don't accept non-existant exercises. Fixes #1520 and #1546.
Implement mark all notifications as read
Fix padding on alerts
Update contributing guide
Fix "about about an hour ago" in notifications
Merge pull request #1563 from slava-sh/master

Fix "about about an hour ago" in notifications