Make the driver firmware-version aware

[kmpeters]

Parameters like E2_AOFFS don't exist in firmware v2.70. Query the firmware version of a controller so that code that is only supported in newer versions of the firmware can be uncommented:

motorAcsMotion/acsMotionApp/src/SPiiPlusDriver.cpp

Lines 461 to 464 in 724020f

	// TODO: re-add E2_AOFFS query after querying the firmware version
	// E2_AOFFS doesn't exist in firmware v2.70
	//status = pComm_->getDoubleArray((char *)absoluteEncoder2Offset_, "E2_AOFFS", 0, numAxes_-1, 0, 0);
	//if (status != asynSuccess) return status;

[kmpeters]

Pull request #46 queries the version string, but doesn't do anything with it other than include it in asynReport output.