Create Admin interface

[Kyle-Falconer]

The admin interface should:

• see the status of all the printers connected to the system (idle/printing/etc)
• change or disable the logo that's printed
• change or disable the QR code generation
• select the page size (Allow for user-selectable printer labels #18)
• choose a printer to be the default for this application (show list of available printers on the system #19)
• configure the Google Sheets upload (authentication, which page to upload to, etc.)
• enable/disable NFC
• configure which parts of the NFC data are printed (Allow admins to change which parts of the NFC data will print #20)
• enable/disable printing
• enable/disable upload to Google Sheets

(check marks above indicate which parts are in progress or complete)