SciDAVis - Improvements SVN-temp

- moving all qtiplot tags to "/tags/qtiplot/"

- creating new "tags" directory

- moving old "tags" to temporary location

Deleted Line/LegendMarker files.

- Renamed LineMarker to ArrowMarker and LegendMarker to Legend.
- Added ImageMarker to the Python scripting interface.
- Improved Python scripting interface and cloning of MDI project windows.

- Fixed displaying of the curve style combo box in Add/Remove curve dialog.
- QtiPlot now saves/restores the size of the Add/Remove curve dialog.

- Improved the Python scripting interface.
- Added the possibility to load and execute a script using the following command line:

qtiplot -x file_name.py

- Fixed a bug in LegendMarker.
- Improved seting of a user defined filter in ImageExportDialog.

- Implemented Feature Request #3476: "better plot Ascii data".
- Partially implemented Feature Request #3511; only the part concerning moving of data points: now one can restrict the movement to horizontal or
vertical via e.g. Alt and Ctrl keys, respectively.

- removed base class QObject from AbstractColumnData
and added method asQObject() instead
- implemented TableAppendRowsCmd
- improved handling of invalid cells
- improved handling of user input
- added "virtual QUndoStack *undoStack() const" to MyWidget
- moved the table undo stack to TableModel
- updated the test program and fixed some bugs