Remove unused code and fix the legend chooser when a layer contains only one or more geometry columns
Merge pull request #572 from ebocher/fix/legendwithoutattributes

Make the legend chooser propose correct thematic maps. 

When layer contains only geometry columns, the legend chooser now proposes only
Unique Symbols, according to the geometry type.

Also remove the following unused classes:
    * orbisgis-view/src/main/java/org/orbisgis/view/toc/actions/cui/LegendListRenderer.java
    * orbisgis-view/src/main/java/org/orbisgis/view/toc/actions/cui/legends/ImageFileChooser.java