Replace default wicket tree icons with Fontawesome icons.
Color scheme used: http://www.google.com/design/spec/style/color.html#color-color-palette.
A lot of nodes now have their own icon. The rule is that an icon matches a certain node type.
Colors are used for different branches. Every branch has its own color. Exceptions are there for specific node types, e.g. hippofacnav:facetnavigation nodes. Also virtual nodes have their own icon and color (orange open circle).