Make inital page configurable

[steve192]

Following usecase: I am using a bluetooth barcode scanner. I used tasker to start grocy automatically whenever the barcode scanner connects to my phone. Ideally I want to start scanning products without touching my phone besides unlocking it. This would be possible if it were possible to configure grocy to start purchase quick mode on app startup.

So my suggestion would be to make the start page / home page configurable