SciDAVis - Improvements SVN-temp

- Added Matrix::cell and Matrix::setCell.
- Some minor fixes.

- Some more code clean-up in MultiLayer.
- Reverted some of Knut's changes in CanvasPicker concerning the selection of layers: now a click on the plot canvas makes the layer the current layer and raises it on top of the layers stack.
- Fixed annoying resizing problems when cloning 2D plots.
- Improved the loading of project files: the ApplicationWindow is only shown at the end, which considerably speeds up the whole process.

- Ported Graph to pure Qt4 and optimized the reading of data from source Tables when performing a plot.
- Fixed a couple of bugs linked to the MultiLayer class and did some code cleaning in this class.
- Improved the layout of the PlotWizard.

- added 2 missing lines in class Table

- fixed compiling errors that were caused by the merging

- updating qt4 development branch

- Added support for compiling a demo version.
- Some minor fixes.

- Derived the Fit class from the abstract Filter class.
- Did some cleaning in the graph.cpp (removed spurious data analysis related methods).

- Fixes bugs in the Axis Dialog.
- Fixes the Format Menu Bar for 2D plots.
- Removed the superfluous insertFirstLayer() function from the MultiLayer class.
- Improved the Differentiation class.

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