Began simple friends implementation.

Friends, once manually added, are now displayed on the friends page.
Completed 'add friends' functionality.

Friends can be added by inputting their username.  Error messages
are generated if you're already friends with the user or they don't
exist.

There is no concept of a pending friend request.  If one person
adds a friend, they're friends.

Viewing another user's profile has yet to be implemented.
Merge branch 'friends'

Conflicts:
	socialnetwork/templates/base.html
	socialnetwork/urls.py