SciDAVis - Improvements SVN-temp

- Ported Differentiation (DifferentiationFilter) and TableStatistics
(StatisticsFilter) to the new framework.
- Added demo/test program for the new filter classes.
- Removed QObject inheritance of AbstractColumnData and corrected inheritance
order in *ColumnData.
- Provided standard implementations for the following methods (so that filters
don't have to bother implementing them):
AbstractStringDataSource::valueAt(int row) const;
AbstractDoubleDataSource::numericFormat() const;
AbstractDoubleDataSource::displayedDigits() const;
AbstractDoubleDataSource::textAt(int row) const;
AbstractDoubleDataSource::constDataPointer() const;
AbstractDataSource::comment() const;