SciDAVis - Improvements SVN-temp

now inherit from AbstractAspect, so that we don't need any
signal-emitter/reciever classes any more.
- Since filters are now Aspects, their ownership can be managed by the
generic mechanisms in AbstractAspect. TODO: implement hiding of Aspects
most users don't need to know about, like input/output filters of columns.
- Eliminated shared_ptr in favour of the hierarchy-based memory management
provided by AbstractAspect.