SciDAVis - Improvements SVN-temp

- Fixed crash when creating a table with given Column objects.
- Fixed performance issue in Differentiation (when applied to large tables).

- Updated download page to point to the LabPlot repository for the development
version.

- Added link to API documentation of the development version.

- Webpage ported to webgen 0.5.x.

- Some pages updated. Better screenshot on index page.

- Removed outdated description of Aspect framework. Will be replaced with an API
documentation for the development version, which is easier to keep up to date.

Update of Spanish translation by Mauricio Troviano.

- 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.