Added Wifi Connect

[steco]

I've tested this on my setup and it looks good, but needs a wider set of tests before we can be confident it covers all use-cases

Some notes

• it checks for a valid wifi connection on startup. If there isn't one it pauses the startup of the Train Display (so the screen will show blank) and instead creates the "WIFI Connect" hotspot. I think we could have it constantly checking for a valid wifi connection if we wanted to
• the image size is now ~220MB, unsure if this will cause problems but there is probably some streamlining we can do

Ref: #145
Ref: https://github.com/balena-os/wifi-connect