Achievement Items

This adds achievement items to the achievement system. Right now they are awarded for earning levels. Once you earn a level you will get a one time use item which has a varying effect. For example, some items extend the due date of a homework, some reset the number of incorrect attempts, and so on...

Other small changes:

-Achievement messages are now shown using a modal popup
-Very basic bootstrap support was added to math3 to make it support modals
-I put jquery in the system.template file and removed all other instances of loading jquery since it was breaking bootstrap
-fixed a bug having to do with checkboxes and the homworkset/classlist editors
-Moved the achievement css stuff into the themes folders