How to setup virtual containers with LXC and quota support on Debian 8

Quota support is an often requested feature in lxc. Linux filesystem quota is required when you want to give multiple users access to a container and want to control that one user is not using all the disk space. Quota is also required for web hosting servers, e.g. with ISPConfig 3, for the same reason: one website shall not be able to fill up the whole disk. This howto shows you, how you can use lxc with hard disk quota using qemu nbd with a qcow image file on Debian 8.