Task for KDE Bugzilla issue: #420373

SUMMARY
Implement Bahtinov focus in Ekos.

Allow focus using a Bahtinov mask. This should be an expansion of the current focus implementation in kstars/Ekos.

As Bahtinov focus is usually done on one star at the time, the auto select star should be disabled, forcing the user to select the star on which to perform the Bahtinov focus algorithm.

For the Bahtinov focus algorithm the algorithm used in the Bahtinov-grabber project can be used (and adapted to fit in kstars/Ekos).

STEPS TO REPRODUCE

1. Point your telescope at a bright star and place the Bahtinov mask on your telescope
2. Start kstars
3. Open Ekos
4. Connect to camera
5. Select focus tab
6. Select detection algorithm Bahtinov
7. Capture an image
8. Select star in image
9. The Bahtinov lines will be shown in the image and the HFR (or focus error) is shown below the V-Curve

OBSERVED RESULT
Not applicable as it is a new feature

EXPECTED RESULT
Assist in focus using a Bahtinov mask

SOFTWARE/OS VERSIONS
All supported OS.