Refactoring the Focus module.

Summary:
This differential relates to tests and code structure for the Focus module.
Tests show that:

• There is no way to determine when the star detection procedure is done. The capture button should re-enable when everything is finished.
• The CCD Simulator needs improvement for some detection mechanisms to work properly.
• It is difficult to create fixtures with deterministic verifications, although better controlling the simulation time should help.
• Syncing the mount to object coordinates is a good idea to speed up tests.
• When not tracking, the CCD Simulator doesn't render trails, it could be a nice improvement.
• Because kstars_ui_tests is becoming larger, it needs to be divided into multiple smaller tests for efficiency.
• QTest, because failing a test means returning from the test function, is macro hell.
• QComboBox is difficult to control programmatically because of its internal signal management.

We then refactor star detection for clarity and consistency in Focus and attempt to reduce side-effects in FITSData:

• Make FITSData buffer read-only, except for DarkLibrary.
• Move Threshold, Gradient and Centroid detections out of FITSData.
• Move SEP detection out of FITSData.
• Docs, copyrights and adjustments.
• Removing expected failure on Gradient/Threshold.
• Adjust KTRY_EKOS_CLICK to use KTRY_EKOS_GADGET.
• Extract star search block to simplify setCaptureComplete.
• Reset KStars time after starting Ekos.
• Fix object fixture builder.
• Slight delay to overcome the weird toggling of the capture button.
• Separate/simplify annulus and threshold tests.
• Delay target chip retrieval when capture is complete.
• Test frame average, extract code averaging HFRs.

Test Plan: Run kstars_ui_tests.

Reviewers: KStars, mutlaqja

Reviewed By: KStars, mutlaqja

Subscribers: murveit, mutlaqja, kde-edu

Tags: KDE Edu

Differential Revision: https://phabricator.kde.org/D28292