Implemented Bahtinov mask focus assistant, fix compiler warnings (in fpackutil.c and modcalcvizequinox.cpp)

Summary:
Implemented Bahtinov mask focus assistant, fix compiler warnings (in fpackutil.c and modcalcvizequinox.cpp)
Added unit test for bahtinov focus assistent
Fix compiler error (comparison between int and double)
Fix compiler error after merge

# Conflicts:
#	kstars/fitsviewer/fitsview.cpp

Test Plan: Tested manually by installing software on Raspberry Pi and connect it to my telescope, pointing to a bright star and check if bahtinov mask is overlaying the diffraction pattern correctly.

Reviewers: #kstars, TallFurryMan, mutlaqja

Reviewed By: #kstars, TallFurryMan, mutlaqja

Subscribers: lancaster, astrorunner, mutlaqja, TallFurryMan, kde-edu

Tags: #kde_edu

Maniphest Tasks: T13035

Differential Revision: https://phabricator.kde.org/D29325