SciDAVis - Improvements SVN-temp

- Implemented saving/restoring of antialiasing settings for individual graphs.
- Improved drawing of ErrorBars and of Bar curves (still not perfect!).
- Moved some of the content in fitclasses to two new files: ExponentialFit and MultiPeakFit (.cpp and .h). Should we do the same for all the other fit classes?

- Fixed restoring of backup files and added an open menu entry for these files.
- Fixed bug in adding error bars.
- Got rid of superfluous "activeGraph" pointer in ApplicationWindow. Modified some functions accordingly (especially the DataSetDialog).

Fixed bugs in changing plot associations for 2D plots.

- fixed loading of spline curves
- fixed loading of project files from version 0.7.8
(I don't know if it works for versions >0.7.8
and <0.8.3 since I don't have the code of those old
versions. The important question is: When were the 2 lines

if (style <= LineSymbols || style == Box)
s+=QString::number(symbol.pen().width())+"\t";

added to Graph::saveCurveLayout(int index).
This decides the first part of the condition
in lines 10165 and 10179 in ApplicationWindow.cpp.)

- Fixes restoring of curve axes for ErrorBars.

- Fixes bug in Interpolation.
- Fixes showing of the fit legend.
- Improved drawing of LegendMarker in order to allow empty lines.
- Fixed ApplicationWindow::windowsList() in order to include hidden windows.

- changed button from "load" to "save" in ImageExportDialog

- Fixes a crash occuring sometimes when opening Notes in old project files.

- Fixed Bug #10422: Bar's error is not shifted on the plot.
- Reimplemented workaround for Bug #8267, using Tilman's first suggestion: symbol_size = 2*chosen_size + 1

- Improved handling of transparency in 2D plots.