New koofr backend - testers needed

#1

I’ve just merged the koofr backend into the latest beta - thanks to jaKa Močnik from Koofr.

From their website:

Koofr offers 10GB of free safe storage for your files with affordable upgrades and options to connect multiple cloud accounts.

The rclone docs can be found here

https://tip.rclone.org/koofr/

Please give it a test and report problems here or make a new issue on github

Thank you!