changing etc/gridvis.conf

To use a system wide project folder we have to change the behavior of
etc/gridvis.conf. Setting the default_userdir to
/var/lib/GridVisProjects and removing the jdkhome setting as we set this
value in the starting wrapper. We have some systems with multiple Java
JRE's like Wheezy.
d/gridvis.desktop: changing binary call

In addition to 3dc8cb4631ec61cb2f13dcb366d6213372a2f77c change the
dekstop file for Gnome Desktops too.
d/g-d.post{inst,rm}: adding postinst and postrm script

For automated use of a centralized project directory we will use a
seperated group 'gridvis-desktop' that will be generated or removed by
the postinst/postrm scripts.
d/g-d-w.sh: expanding the starter script

The starting script is expaneded to do some sanity checks after adding
the the implementation of the postinst/postrm scripts.