add dep for libgconf for rpi
A user reported the following after trying to run a freshly installed Purr Data deb on RPI:
pi@raspberrypi:~ $ pd-l2ork
guidir is /usr/lib/pd-l2ork/bin
priority 6 scheduling enabled.
priority 8 scheduling enabled.
/usr/lib/pd-l2ork/bin/nw/nw: error while loading shared libraries: libgconf-2.so.4: cannot open shared object file: No such file or directory
watchdog: signaling pd...
watchdog: signaling pd...
watchdog: signaling pd...So we should probably put libgconf as a dependency in the deb