added ability for users to 'purchase' items for others.
intermediate commit for beginning adding purchases destroy method
Refactor purchased_by migration for compatibility with Postgres
changed purchased_by typo to purchased.
removed purchased from items _form to fix bug where edit does not work.
Merge branch 'master' into purchases
passing delete tests for users to be able to undo purchased Items.
added jquery to purchases to allow users to set purchases to nil if they wish to undo them.