loadLandscapeSIG: Create a Landscape object from SIG shapefile file
Description
Create a Landscape object from SIG shapefile. Shapefile has to contain a SpatialPolygonsDataFrame. Data in the data frame contain fields (polygons) information. Row names as fields ID, cols names as sources | neutral | receptors (for a given field, the value is 1 for the type of the field (source or neutral or receptor), otherwise 0).