Ref #2 - user/index shows friend status correctly

-Added some class methods to Friendship model, in order to grab
friendships of different types (accepted, pending, owner of friendship)
-Expanded the 'is_friends_with?' method to not only find a friendship
with the given user_id, but also determine if its been accepted or
pending using the new Friendship class methods.
-Updated the conditionals on the user/index page to display different
links depending on the status of the friendship