New GRBL initialization protocol

[breiler]

Changed the protocol for initializing GRBL controllers. Instead of relying on a welcome string when connecting to a controller it will do a series of commands to initialize the connection. It will no longer try to reset the controller on connect.

1. Try and query the controller with ?
2. If the controller is in a HOLD or ALARM state, send an empty line to see if the controller is responsive
3. Query the build information to get the controller version $I
4. Query settings $$
5. Query parser state $G

This should fix the problem when connecting to GRBL Mega 5x which would just hang when connecting. It will also work better with grblHAL which doesn't require a reset.