First smooth working of both UARTs simultaneously and external power circuit

I got the modem + GPS + USB logging working smoothly. I’m stepping away from ChibiOs for now, because I can get something working well using serialEvent (the internal loop is executed at 250 kHz). The power module is working ok, based on a Recom R.78. The decoupling capacitor is installed on the power output, but decoupling capacitors on the load are yet to be added.