Do not send AXSDEF command to Gx6K controllers

All GT6K controllers are stepper controllers whereas all GV6K are
servo controllers. In contrast to the 6Ks they cannot be configured
to be one or the other. Check the controller model using the TREV
command to detect if we are connected to a GT6K/GV6K controller and
do not send the AXSDEF command on these devices (it is not supported
on these and causes error messages).
Merge pull request #10 from mark0n/fixAXSDEFissueOnGT6K

Do not send AXSDEF command to Gx6K controllers
Remove some lines that initialized settable parameters in the constructors. This was preventing setting default values via the database.
Allow soft limits to be disabled

Set DHLM to "inf" and DLLM to "-inf" to skip configuration of soft
limits.
Merge pull request #13 from mark0n/disableSoftLimits

Allow soft limits to be disabled
Fix S curve acceleration issues

Ensure the values send with the A and AA commands always satisfy
the following condition: 1/2*A <= AA <= A. If this is not the case
the motor controller responds with an "*INVALID CONDITIONS FOR
S_CURVE ACCELERATION" error.
Merge pull request #14 from mark0n/fixAccelBug

Fix S curve acceleration issues
Improve check of S curve parameters
Provide warnings if S curve parameters are not set
Increase accuracy of data sent to the controller
Merge pull request #15 from mark0n/s_curve_param_check

improve S curve param check
Merge pull request #16 from mark0n/increase_max_digits

Increase accuracy of data sent to the controller