Svg library cleanup

Cleanup of the SVG Library as discussed here : http://osgeo-org.1560.x6.nabble.com/Ideas-on-the-SVG-symbols-library-td5040508.html

This is not totally ready yet (I forgot a few icons), so it shouldn't be merged, but is ready enough for comments / ideas...

What do you think ?

It seems the UI for setting svg colors is a bit buggy (sometimes colors are reset when opening the dialog).
It also seems that the marker's color isn't applied to the SVG like it is to "simple markers", making the use of the SVG params almost useless with color ramps.