Rewrote receipt PDF generation method to work with part main_info property
   calpoly/frontend/__init__.py: Added engineering_notation function to jinja2 templates
   calpoly/frontend/frontend_misc.py: Rewrote receipt generation method
   calpoly/frontend/templates/receipts/single_receipt.html: Used main_info property of parts instead of just category and manufacturer part no
   calpoly/parts/utils.py: Added engineering_notation function here
   deleted:    calpoly/users/utils.py: Removed engineering_notation function from here
Add 'parts_seller' role to 'webmaster' function.

calpoly/frontend/frontend_misc.py: PEP8.
setup.sql: Automatically add the role
'parts_seller' when executing the webmaster
function