Add support for additional EGM modes

[jontje]

As per title.

Currently unsupported modes are:

• EGM Path Correction
  Path correction can be used to correct a programmed robot path (requires using special RAPID move instructions).

• EGM Position Stream (requires RobotWare 6.07 or later)
  Position streaming can be used for when it is only interesting to track a mechanical unit's position, and not to control it's motion.

This can for example be done by implementing additional EGM interface classes.

[gavanderhoorn]

@jontje: this should now be possible with the merge of #32 right?

[jontje]

Yes it is

[gavanderhoorn]

@jontje: is there still work to be done here?

[jontje]

I will not be implementing support for EGM Path Correction anytime soon.

Regarding EGM Position Stream (i.e. only get feedback from the robot, and not send commands), then it works with the current EGMControllerInterface class. However, it might be nice to create an EGMStreamingInterface that only exposes a read method.

I also intend to implement support for external axes, which at the moment needs to be controlled in its own RAPID motion task (the abb_libegm classes currently only work when a six or seven axes robot is "on the other end"). And here it might also be nice to implement an EGMExternalAxisInterface, which doesn't expose the Cartesian write methods.