Whole bunch of things

- Added numeric only validation for quantity in the parts page
- Handled the empty cart condition
- Renamed the option name to Category and added it to the cart display,
so in future if we decide to add more attributes to the part and want to
display in the cart we do not have to change the view
- Added a begin checkout page
Cart empty message added
Checkout working

-Customer can enter their name and email and checkout.
- Shows them a confirmation page
- Updates database records