Added determine_scalebar_length method to LayeredBasemap.
Set transparency for thematic legends in draw_legend method of LayeredBasemap.
Improved draw_scalebar method of LayeredBasemap, allowing position to be specified in axis coordinates.
Fixed return value of map_to_display_coordinates and map_from_display_coordinates methods of LayeredBasemap.
Added display_from_ax_coordinates, display_to_ax_coordinates, lonlat_from_ax_coordinates and lonlat_to_ax_coordinates methods to LayeredBasemap.

git-svn-id: https://svn.seismo.oma.be/svn/seismo/mapping/layeredbasemap/trunk@7647 40b490c5-b4d9-47cb-8714-9bef99b524d5