+ added PropertyWidgetFactory
 + added AbstractPropertyWidget and StringPropertyWidget
 * replaced own observer implementation of AbstractPipeline and AbstractProperty with sigslot
 * changed PropertyCollection (aggregation) to HasPropertyCollection (inheritance)

git-svn-id: https://camplinux.in.tum.de/svn/campvis/trunk@207 bb408c1c-ae56-11e1-83d9-df6b3e0c105e