remove style property in favor of symbolizers

[tschaub]

We currently use the property name "style" to represent a symbolizer in many places. In addition, we use the property name "symbolizer" in some places to represent an object referencing multiple symbolizers (Point, Line, Polygon).

This should be cleared up. I'm in favor of giving a rule a "symbolizers" property. This would always have Point, Line, or Polygon properties (or Text when we support it). This lets you draw your points with a different stroke width than your polygons (for example).