SciDAVis - Improvements SVN-temp

- Added compile-time option for choosing to always use the compiled-in path to
the manual instead of the user-configured one. Useful if packagers also
include the manual and want to push a changed path to their users.
- Choosing the path to the manual after SciDAVis failed to open it now uses
chooseHelpFolder() instead of implementing a slightly different procedure for
doing the same thing.

- Fixed handling of comments in muParser expressions. Closes bug #2820913.

Improved handling of plot tools:
- Allow different graphs to have plot tools active at the same time, making
sure that the tool buttons are updated when switching windows.
- When the data picker tool is active, up/down arrow keys switch between
corresponding points of different curves if possible instead of switching
to the first data point. Useful when comparing curves with the same X values.

- Fixed importing a table via Python with fewer columns than the target.

- Fixed unintended re-ordering when plotting multiple columns at once.

- Fixed one instance of bug #2811820. Crashes occured reproducibly when moving
a window to a folder and than removing that folder.
- Fixed a crash in Graph::insertCurvesList() occuring when the list of columns
to plot includes invalid entries (e.g. due to a mistake when plotting from
Python).
- Added enum QwtPlot::Axis to the Python API. API functions working on axes
expect the axis to be given as an integer corresponding to values of this
enum; and using the numbers directly is hard to read and write.

- Fixed bogus comment in scidavis.pro.

- fixed bug #2819887: Error bars aren't automatically added to graph

- MDIWindow.setName() diverted to ApplicationWindow::renameWindow(), which handles crucial parts of the renaming process.

- Fixed minor issues with the German translation.