Fix the mess rebasing caused (why?)

Maik's review and rebase

remove unrelated changes

You can have a situation where name.tif has tag A and name.dng tag B. With name.xmp scheme the information in the database will then be inconsistent with the information in the file. It is essentially a race which is written to xmp first, i.e. when writing information from db to file metadata, whether name.xmp ends up with tag A or B is random. I don't know whether it will create problems with the execution, but I wouldn't be surprised.
A simple way to minimize this risk would be to only allow "name.xmp" scheme when the option to write to xmp for raw formats only is checked. Unless someone converts from native raw to dng it is rather unlikely, that there will be a naming conflict.

As far as I see this does not handle/prevent/... the case where there is two different files with the same name but different extensions (e.g. name.dng and name.tif) - am I missing something?

This is actually purposely not explicitly set as required, such that all dependencies get checked before aborting. The presence of Qt5 (and other required libraries) is checked later further down.

digikam doesn't use kdcraw, so we are not the right ones to review this.

Thanks!

No idea what the correct workflow is, but if you have commit access, ship it.

Was committed by R482:0c7e25df54de.

You should write to the developer mailing list (digikam-devel@kde.org) to get attention for this.

As you may have noted, the digiKam project isn't (yet?) active on Phabricator. To get feedback, open an issue in bugzilla (maybe linking here).
I don't know anything about QML and almost nothing about KIPI, so can't really be of help.