new opencpn and pypilot plugin

[seandepagnier]

I have fixed the nmea processing today. It's been really difficult because the serial drivers in the kernel have some bugs which actually crashes linux in some cases. I'm trying to work around this and a few other strange issues so it's delicate.

I suggest you just use a second sd card, this is by far the simplest. tinypilot is not set up for dual boot and I doubt it will ever be supported. With openplotter it should be possible but a lot of work.