Add jograte and sliders to Control Frame

Allow user to specify the jog rate rather than default to
the maximum machine jog rate.  Values above the maximum
machine jog rate will be capped by the controller.  Only
positive float numbers are allowed.

Added Z and XY slider controls to permit easier distance
adjustments via a mouse.  The sliders have user defined
stops along a logarithmic scale.  Adjustments by the
sliders are reflected in the combobox values.  Adjustments
via the keyboard +-/* strokes are mirrored in the
sliders.  The Z distance controls can be linked via the
Z combobox XY selection.

 Changes to be committed:
	modified:   bCNC/ControlPage.py
	modified:   bCNC/bCNC.ini
	modified:   bCNC/controllers/GRBL1.py