Capture counting corrected if more frames exist than necessary

The last fix to capture counting had some unexpected side effects:

• If using the "Remember job progress" option and there exist already more frames than required, the scheduler displays the full number of existing frames and does not limit it to the maximum that are required.
• If using the "Remember job progress" option and the "Repeat until terminated" option, the Scheduler shows always 0 frames, even if some frames are already present.
• If not using "Remember job progress" with the "Repeat for" option and more than one iteration, the scheduler deletes the running scheduler job after the first iteration.
• The estimated time for sequences that have multiple occurrences of the same signature (e.g. RGBRGB), the time estimation to completion was wrong.

Besides the fixes for this, this MR contains test cases covering (hopefully) all combinations of the "Remember job progress" option and the job completion options of the scheduler.