Guide module: Dither by target drift

Is your feature request related to a problem? Please describe.

If the CCD module plate-solved each acquired image, the Guide module could use this information to correct target-drift through occasional "dither" commands instead of more disruptive "Align" actions in the Scheduler.

Describe the solution you'd like

1. Add a toggle (default: disabled) to the Guide options, within GUIDE_TAB->Options::Guide::Dither, to Correct Primary Scope Drift when performing a dither action
2. At each dither action, evaluate the J2000RA/J2000DEC of the sequence target against the RA/DEC of the most recent result from the solver.
3. Calculate a dither request that re-centers the target, accounting for the dither settings, using guide-pulse commands.
4. If the user just wanted drift correction, with no effective dither, Dither Pixels could be set to zero. The frequency of the correction could be controlled by the Dither Frequency setting.

Describe alternatives you've considered

While the hardware solution is to use an Off-Axis Guider, that option isn't always available to the user (i.e., for a Celestron RASA), where external guiding is required. To-date, I've mostly just accepted that long exposures will produce less than a full usable frame, as the drift areas can be cropped out. An interim solution with existing features would be to schedule smaller sequences with more frequent ALIGN steps, but this introduces additional delay, and potentially greater chance of sequence abort with success of the align/track/guide steps required at each iteration.

Additional context

This feature has a prerequisite of implementing Enhancement #59