Add Bluetooth support for external thermal printers

[pretyflaco]

I sourced a mobile netum thermal printer that can be connected with bluetooth for $20 USD.

There are many cheap offers for these and they are widely available. If we had support for these, they could be a cost-effective alternative for printing receipts and vouchers.

[agbegin]

For reference, Adam from Coinos has worked on this problem https://www.youtube.com/watch?v=JiGoOJZUrP8