Dithering while crossing the meridian recognized as guiding

Summary:
Restarting guiding after a meridian flip currently currently only happens, when the guider is in the guiding mode. For example, in the case that the meridian is crossed while dithering, the capture module does not recognize this as part of the guiding procedure and hence does not restart guiding as soon as the meridian flip is finished. This change fixes this and considers dithering, but also re-acquiring and calibrating as an indication that guiding should resume after meridian flip.

As a side effect, this fixes also the situation when dithering fails in the middle of a capture sequence. Without this fix, a failed dithering is ignored and capturing resumes without restart guiding.

Additionally, a possible a weakness that may cause null pointer exceptions in starting focus execution is fixed. And last but not least, some dead code has been eliminated.

And last but not least, dead code is removed.

Test Plan:
Test case 1: Enable dithering, move the scope close but east of the meridian and start a capturing sequence. In order to ensure, that the meridian is crossed while dithering, run kstars inside the debugger and set a breakpoint before the call of dithering. Check, if after the meridian flip guiding is restarted.

Test case 2: Enable dithering and create a schedule that uses a capture sequence with more than one capture. Start the schedule and interrupt guiding after the first capture while dithering. Check, if capturing and guiding resume. Test this with and without the option for aborting guiding after dither failure set.

Reviewers: mutlaqja, lancaster

Reviewed By: mutlaqja, lancaster

Subscribers: kde-edu

Tags: KDE Edu

Differential Revision: https://phabricator.kde.org/D25105