Fixes bugs in SQL install and moves auth token verification to Auth model.
Refs #31, moves Auth model to PDO from mysqli.
Refs #31, changes User model to use PDO instead of mysqli.

I also removed the PDO::PARAM_* optional parameters from PDOStatement->bindParam() because they don't actually make the queries safer and I'm just going to forget to put them on some of the function calls.
Refs #31, changes Conversation model to PDO from mysqli.
Refs #31, converts Follow and Star models to PDO from mysqli.
Refs #31, moves MediaFiles, Tag, and Upvote models to PDO from mysqli.
Refs #31, changes Message and Notification models to PDO from mysqli.
Refs #31, moves PostFeed, Post, Riff, and UserFeed to PDO from mysqli.

These are the last models that still used mysqli, so after some testing this will be ready to merge with master.
Refs #31, fixes some bugs in mysqli to PDO conversion.
Refs #31, changes positional to named parameters in queries and fixes other bugs.
Refs #31, fixes a few small bugs in queries.
Refs #31, replaces bindParam with bindValue globally.

Using bindParam was causing type errors where an int would be bound to a PDOStatement and then after execution it would be
converted to a string. This caused notifications to be sent of users upvoting their own posts because the === failed due to
types being different.
Merge pull request #56 from RyffProject/mysqli-to-pdo

Refactor mysqli to PDO database driver.