Paintop presets referencing brushes in files are not portable

[LukasT.dev@gmail.com]

> > Currently we address the gbr brush in preset by full path. We might use
> > just a name.
> 
> Well the problem is that two different brushes could have the same name.

I have idea for it. Krita is looking for the brushes in some specified paths 
(user brushes, installed brushes, create package, maybe some other I haven't 
noticed yet). Let's just save the name of the brush like 

<brush filename="coolBrush.gbr" md5="58afe7e809d281fb421e728363bd80cc">

Where md5 is the finger print of the gbr/abr/anyOtherFormat brush file content. 
Because it might happen that you name some brush with the same name in user 
brush dir and in installed brush dir. We would look for the brush where md5 
and name match.

Sven filled the bug report, that's why I'm opening this topic again :)
https://bugs.kde.org/show_bug.cgi?id=250675