Show stops in marble using updated OpenStreetMap data engine

- New action in context menu of route items
- Only shown if the openstreetmap data engine is installed
- New source for the openstreetmap data engine: "getCoords", used by the
applet with source names like "getCoords publictransportstops [stopname]".
Doesn't always work, because the stop name must match exactly and shouldn't
exist multiple times, eg. in different cities.
Uses these filters with jxapi: [public_transport=*], [railway=tram_stop]
- Change OSM url from xapi.openstreetmap.org to jxapi.openstreetmap.org
(not so overloaded server and new implementation in java)
- Plus: Route stop marker items now clipped and with an elliptic shape