apt-repo enhancements: optional args and others

* related to point 4. at #886: optional args for jre and openhab runtime.
* init script ensure cwd == openHAB installation dir
* sources list template: if this file is accessible from the download server registering the apt-repo using sudo will work:
cd /etc/apt/sources.list.d/
sudo wget http://<openhabDowloadSite>/apt-repo/openhab-<version>.list