Added listeners to commands to listen for when it completes.

[breiler]

I started working on a new controller implementation and found a need for listening to if a command was completed.
This could be done using a UGSEventListener and listening for a CommandEvent in the application, but not from the controller. From the controller we have access to the ControllerLisener but would require to implement a rather large listener interface.

I propose to add a listener to the GcodeCommand, this would it make it possible to execute a command and wait for it to be completed:

try {
  GcodeCommand command = new GcodeCommand("G0 X10 Y10");
  ControllerUtils.sendAndWaitForCompletion(controller, command, 1000); // Wait max 1000ms for the command to complete
  if (command.isOk()) {
    // Do something with the response
  }
} catch (RuntimeException e) {
  // The command has timed out
}

[codecov-commenter]

Codecov Report

Merging #1809 (b517f8b) into master (ff31d88) will increase coverage by 0.13%.
The diff coverage is 74.57%.

@@             Coverage Diff              @@
##             master    #1809      +/-   ##
============================================
+ Coverage     18.20%   18.33%   +0.13%     
- Complexity     1914     1938      +24     
============================================
  Files           698      699       +1     
  Lines         29423    29466      +43     
  Branches       2314     2318       +4     
============================================
+ Hits           5355     5403      +48     
+ Misses        23618    23613       -5     
  Partials        450      450              

Impacted Files	Coverage Δ
...om/willwinder/universalgcodesender/TinyGUtils.java	65.21% <0.00%> (-0.36%)	⬇️
...inder/universalgcodesender/AbstractController.java	65.41% <66.66%> (-0.26%)	⬇️
...llwinder/universalgcodesender/TinyGController.java	44.50% <66.66%> (+1.64%)	⬆️
...inder/universalgcodesender/types/GcodeCommand.java	74.28% <72.00%> (-5.03%)	⬇️
...er/universalgcodesender/utils/ControllerUtils.java	76.92% <76.92%> (ø)
...illwinder/universalgcodesender/GrblController.java	55.35% <100.00%> (+0.26%)	⬆️
...nder/universalgcodesender/GrblEsp32Controller.java	93.93% <100.00%> (+10.60%)	⬆️
...com/willwinder/universalgcodesender/GrblUtils.java	72.50% <100.00%> (+0.10%)	⬆️
...inder/universalgcodesender/SmoothieController.java	11.26% <100.00%> (+11.26%)	⬆️
...der/universalgcodesender/ConnectionWatchTimer.java	54.54% <0.00%> (-9.10%)	⬇️
... and 6 more

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