Add GitHub actions

Take inspiration from the workflows used in gohci and bootstrap but
disable many checks because it's going to take a while to fix them all.

Update go generate to make it work without prerequisites preinstalled.

Remove the corresponding checks from .travis.yml. There are still checks
that haven't been transitioned, this will be done in a follow up.

devices/lepton/cci/cci.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
-// "stringer" can be installed with "go get golang.org/x/tools/cmd/stringer"
+//go:generate go get golang.org/x/tools/cmd/stringer
 //go:generate stringer -output=strings_gen.go -type=CameraStatus,command,FFCShutterMode,FFCState,ShutterPos,ShutterTempLockoutState
 
 package cci