Add optional tcp support for connecting to grbl (plus other small improvements)

[garuma]

Make a simple series of change to support connecting to gRBL remotely in addition to local serial (essentially just proxying over a tcp socket). This allows one to use a simple proxy box (like a Raspberry Pi setup with something like ser2net) and avoid having to keep your CNC connected to the main machine.

I had to make some other changes to the project file to be able to compile successfully but I can pull them out if desired.

I added a text input in the settings pane to be able to specify the host:port combo:

I have been using this functionality myself for the past few months without issues with a Raspberry Pi 3 and ser2net setup with this configuration:

6778:raw:6000:/dev/ttyUSB0:115200 8DATABITS NONE 1STOPBIT