[openlayers-parser] Fallbacks of geoserver-specific WellKnownNames

[jansule]

With the upcoming merge of #25, geostyler-openlayers-parser tries to parse a subset of geoserver-specific WellKnownNames. Following problems and fallbacks exist:

readStyle():

• Cannot distinguish between shape://carrow and shape://oarrow. Fallback: shape://carrow
• Cannot distinguish between Circle and shape://dot. Fallback: Circle
• Cannot distinguish between Cross and shape://plus. Fallback: Cross
• Cannot distinguish between X and shape://times. Fallback: X

writeStyle():

• Cannot write style for shape://oarrow. Fallback: use shape://carrow style