Internal guider didn't take binning into account when computing arc-seconds

Summary: Added binning into the arc-second calculations.

Test Plan:
Should see the RMS error for guiding double when binned 2x2.
Probably will also affect the control algorithm.

Reviewers: mutlaqja

Reviewed By: mutlaqja

Subscribers: kde-edu

Tags: KDE Edu

Differential Revision: https://phabricator.kde.org/D29426