SciDAVis - Improvements SVN-temp

- fixed missing "public:" in CopyThroughFilter
- added ": public QObject" and "Q_OBJECT" in AbstractColumnData
again since it won't compile without
- replaced DateColumnData and TimeColumnData by one class
DateTimeColumnData which can store both times and dates
- added ReadOnlyTableModel
- added a small test program for ReadOnlyTableModel
- replaced at() by value() in all ColumnData classes

Added labels to input ports of filters.

- Improved documentation of filter classes.
- Added convenience overload for AbstractFilter::input().
- Added DoubleTransposeFilter and a demonstration of how to combine it with StatisticsFilter for row statistics.
- Added QwtDataFilter, a small glue class for Qwt.

- Fixed several technical problems in the Docbook sources.
- Added auto-generation of Qt Assistent profile (for OpenJade).

- Implemented feature request #3443 (better default paths on Linux).
- Fixed MultiLayer layout problem with Qt 4.3.0.

- Fixed Bug #11220: Segv when changing table/column names.
- Fixed bugs in deleting project folders.
- Fixed crashes in Table::sort() due to a bug in Table::loadHeader()

Solved some constness problems and improved test program.

- Added an improved base class for filters (AbstractFilter).
- 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;

- Fixed a bug in TableStatistics.
- Added svg to the QT options in qtiplot.pro (needed with Qt 4.3)

- renaming TableDataModel to TableModel (part 2)