Slovenian language files

[gresakg]

Added Slovenian language files, fiew fixes and updated README.md

[tpokorra]

Hello,
thank you for the pull request!
I have not had time to completely review it.
On the other hand, my changes are based on https://github.com/umount/message_label, and I wonder which project is "upstream"?
I have to say that I probably won't be using the message_label plugin for my own deployment, so I have not much interest in maintaining it.
But I am glad if my changes are useful to you!
All the best,
Timotheus

[gresakg]

Hi,
I usualy make pull request to the forked repo which in this case was yours.
If you wish, you can accept the changes and than push them upper upstream.
Except for the language file, my changes are purely cosmetic :)
Regards, Gregor