Reactivate threshold function

[AxelHamburch]

With the introduction of the new bitcoinSwitch web interface from version 0.1.0, the threshold function seems to have been lost. The program code for reading the variables from the memory was completely missing. I have now updated this again.

Furthermore, I have added a few optimizations for the user feedback. Especially the feedback that the serial interface is ready to receive the upload data must be clearly displayed to the user.

I have included the previous PR “#46 force wifi scanning” here, as it makes sense and works.