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