SciDAVis - Improvements SVN-temp

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)

- renaming TableDataModel to TableModel (part 1)

- renamed rowString/rowValue to textAt/valueAt
- implemented handling of QLocale in string and double columns

Improved Installation instructions for Linux.

- Fixes bugs in importASCII introduced by my last commits.

- Fixes bugs in importOPJ.cpp introduced by my last commit.

- Implemented opening of .ogm and .ogw files as new windows instead of new projects.
- Improved the Day/Month column format.
- Implemented Feature Request #3435: Only 2 fitting points at linear fits.