Add current_user helper method, change session clear to delete id
Add score model and migration
Fix score migration and change deck and user models to connect with score
Increment scoring for correct answer

Choosing the desk starts a score instance for that desk for the current user.
Add scoring and alerts as of presentation
Merge pull request #28 from mathildemouw/scoring

Done
![img](http://31.media.tumblr.com/3e668abd8578556b624ed0af09dce10e/tumblr_mwn18umvbM1rdh9azo1_500.gif)