Delete items page

#258 Should be merged before this. 

*Adds a js-based admin page for (almost) all db items. Currently ReceiptItem and TimeSlot are not included because they require primary key revisions
 *Currently only supports delete operation
*Made backend db objects and api much more uniform.
*Reorganized various utils.py files to remove circular dependencies and put functions in more logical places. 

The JS console is a proof of concept idea basically, but the work done on the db objects is important and should be merged regardless.