SciDAVis - Improvements SVN-temp

- Reduced memory usage during save and restore of large tables. This avoids
crashes observed on Windows for projects on the order of magnitude 100MB.
Closes bug #2897197.

- Update of Spanish translation (thanks to Mauricio Troviano).

- Implemented access to Y columns based on lookup in corresponding X column.

- Fixed some cases of messed-up axes after changing curve data.

- Consolidated code for loading data into curves, fixing many inconsistencies.
Closes bug #2872732.

- Integration code rewritten, user interface changed to provide control over the
interesting step (interpolation). Instead of numerically integrating the
interpolating polynomial (!) we do this step exactly (thus, no need for
integration method options any more).

- Removed some stale code.

- Fixed labels in LineDialog.

- Fixed bounding rectangle of XYAM vector curves.

- Fixed bug in (auto)correlation function.

- Update of Czech translation by Pavel Fric.