Relented on beta warnings

Well, my attempt to keep people from shooting themselves in the foot when upgrading to the beta version of ReceiptWallet has back fired. I've had few people download it (partly because of mistakes I made) and others have had problems reading the text. So, I've relented and now allow automatic updates. However, the first time a new beta version is run, the user is presented with a warning that hopefully makes things clear.

BetaWarning.png

I'll see how this pans out in terms of people trying the beta.