Add basic comments mailer
Remove unneeded includes
Add after_save observer for comments
Fix comment mailer test

Turns out the includes are actually required. (2844e1a)
Fix hound suggestions
Fix failing tests
Add comment notification toggle to user profile
Add observer to observer list

Without adding the observer to the observer list, the comment creation
is not being observed.
Fix law of demeter warning

The law of demeter states that an object should only know about its
closest relatives. Don't call methods through other methods.
Fix failing observer test (removed it)
Merge pull request #973 from BiteKollektiv/add-comments-mailer

Add comments mailer