First bunch of opencl 46 suggestions

[jenshannoschwalm]

• preferences
• setting up

@elstoc had messed up my authentication stuff ...

[jenshannoschwalm]

BTW - have just seen that you included lens vignetting and the backthumbs crawler stuff already. Do you have any questions about that or other things i left undocumented?

[elstoc]

If you could look over the stuff I've done and let me know if it needs anything more that'd be great. If there's anything more that's undocumented it's because I haven't started looking at it yet, so I don't yet know if I have questions.

[jenshannoschwalm]

No, I checked my to-do list for updated dtdocs and there is only opencl stuff left out.

[elstoc]

Are you expecting to push some changes to the performance tuning section as well, to cover these alterations and those in https://github.com/darktable-org/darktable/pull/15166?

[jenshannoschwalm]

Are you expecting to push some changes to the performance tuning section as well

Absolutely!

[jenshannoschwalm]

The second commit is about the device tuning ... checked for correctness, added some hints / suggestions.

1. Feel free to change style whatever you think is best
2. Let me know about things you are not sure about ...

[elstoc]

Nice, thanks. I'll take a look at it this weekend

[jenshannoschwalm]

More fixes, squashed and force-push a single commit for easier reviewing.

I think the only opencl topic missing in this pr would be sheduling profiles ... That is certainly just partly wrong since some dt versions and needs some caretaking. As i don't use multiple devices myself it will need some testing and code reading, will likely be able to do that on the weekend but in another pr.

[elstoc]

LGTM thanks!