Enforce UTF-8 no BOM on files

[krwq]

We should remove BOM from all files and add some enforcement so we don't change it back by accident.

[gfoidl]

some enforcement so we don't change it back by accident

Is .editorconfig enough for this?

[krwq]

yes, we currently enforce reverse :-) we need to convert all files as part of this issue :-) Better if we add some simple check as part of the build (not required though to mark this as complete)

[pgrawehr]

Do we have a documentation why this should be an improvement? I'm still fearing that removing the BOM will result in different editors/OSes breaking non-ascii characters in our code files. And we have quite a few of those.