Add definable jog buttons.

[RyanParle]

Sometimes it is handy to be able to move an axis in discrete steps rather than on a jog wheel. for example using a linear rail for macro focus stacking where you wish to position the camera precisely & then set up a move over a small distance.

i suggest an additional jog button for movement in each direction and a numeric value entry to define the distance to travel per click. Personally i would locate the new buttons just below the jog wheel with the buttons on the side of the panel corresponding to the direction of travel & have the jog distance value entry located between the two jog buttons.

Ideally the units used should correspond to the units set by the device lookup tables suggested in issue #13