Bug fixing capture refactoring

Bug fixes for the code refactoring unifying capture initialization for new sequences and continuing of sequences:

• pending tasks check before continuing made frame type specific
• stop looping messes up the state

Test plan

1. flat frames: Create a sequence job for flat frames with manual flat source, target ADU=3000 and Tolerance=1000. Run the sequence and check, whether a) a modal dialog appears asking for scope covering and b) the configured flats are generated.
2. bias frames / dark frames: similar tests as flat frames.
3. simple looping: select frame type "light" and press the looping button. Verify whether the looping runs as expected and aborting works.
4. looping with job list: Add a flat frames job to the sequence queue. Select frame type "light" and press the looping button. Verify whether the looping runs with light frames and aborting works. Try the same with executing the sequence queue first, then change the frame type to "light" and start looping.

If this works as expected, re-test the light frames tests from merge request !9 (merged)