Allow side depending attributes in mappaint

[stoecker]

Although unwanted by some OSM members tags depending on way direction exist in certain fields. JOSM should have a way to display such at least as map overlays beside the ways. So the XML for mappaint should support side dependency. E.g. using keywords like left and right.

I till now found no way to have the drawing routines doing that automatically except drawing the waysegemnts using shifted coordinates which certainly will have some unwanted side effects.

This style would allow to support all forms of left,right,forward,backward in tags.