How to create a background:
~~~~~~~~~~~~~~~~~~~~~~~~~~~

1. Create a new class, with the data which is required for the
background and a member function to parse the data out of an xml
file, the class needs to inherit from BackgroundData

2. Create another class, which inherit from the data class and from
"Background"

3. Add the new class to the class chooser in
BackgroundData::parse_... and Background::create(BackgroundData)

EOF
