Major changes:

• Introduce the smoothLayer function, this function computes smoothed maps of potentials. It uses quickStewart from SpatialPosition package.
• Most of previously suggested packages are now imported.

Minor changes:

• Introduce the legend.*.values.order parameter in typoLayer, propSymbolsTypoLayer and gradLinkTypoLayer. This parameter allows to order modalities in the legend and eases the color assignement.
• Change min value in prop*Layer legends.
• Suppress zero values in propSymb*Layer.
• getGridLayer is faster.
• getLinkLayer is faster.
• getBorders is faster.