Fix shebangs and executable bits

[VojtechStep]

The part of #210 which touched on the executable bits never got resubmitted. I decided to follow the explanation from there:

• files in data/ have not to be executable, they are templates, if you read there contents you will see they can not work.
• files in session_scripts should be executable indeed
• it seems that src/bin/utility_script_start.sh is not used at all, it could be removed
• files in src/jack_config_script have not to be executable, they are loaded by those that are.

The first is no longer true, so I kept the executable bits. The second and third one are addressed.

I'm confused about the config scripts: @Houston4444 says that files loaded by executable scripts don't need to be executable, but e.g. load_config.sh is executable but also sourced from script_starter.sh. Is that an error? Or are other scripts besides script_starter.sh also supposed to be started as standalone scripts?

In any case it makes sense to me that a file should have a shebang only if it's executable, so I removed the shebangs from non-executable files. Depending on clarification on the paragraph above, I expect to make more scripts non-executable and remove more shebangs before this PR is merged.

I also made all the scripts in src/bin with shebangs executable, though I'm not sure if conf_testou.py and qt6_app.py were intended to be added in the first place.

Also let me know if the whitespace fixing commit should be dropped.