Ian/remove scan

Tried a few things, ended up going for the least invasive way to remove scanning. When Nico is back we'll talk about the best way to clean all the scanning code up. Its ready for review, i've tested it with my dexcom, plugin it in before starting the extension and while the extension is started, works for me. I cant try it on windows. Maybe @HowardLook can try. cc @jebeck @jh-bate @kentquirk