Added table friends to db

Has 2 varchar fields, user and friend.
Both have a foreign key on users.username
Rewrote friends API logic

POST requests must include parameters:
do: set/add/remove
friends: friend(s)'s username(s)
Updated profile logic to new friends API

Updated SQL queries
Added friend button, closed #31
Updated loadquestions to new friends API

To do:  reportq, viewq, sent, search
Small improvements at friends.php

On exception set http response code to 400/500
Make the form .scriptOnly
Add cols and rows to noscript textarea
Updated reportq, viewq to new friends API
Updated search, sent to new friends API
Backticks around user in queries

User is kind-of reserved in mySQL
Removed field friends from table users
Merge pull request #34 from anestv/friendships

Store friendships in another table