More flexible processing vector layers

For any vector input mapMCDA currently considers only its geometry and computes the distance map to the spatial features it contains, disregarding its attribute table, if any.

However, sometimes users need to use some spatial variable that is spatially aggregated into an attribute of some vector map. They need to rasterize the attribute externally and feed the resulting raster into mapMCDA.

We could offer the possibility of doing this automatically, at the moment of scaling. We can default to the current distance map and, whenever there is an attribute table, offer the possibility to rasterise any of the quantitative variables.