Move getIcon function to massTransitStop
Determine used image icon in getIcon function if possible
Determine used image icon in getIcon function when switching types
Determine icon in getIcon without external input
Remove unused marker properties
Extract marker creation to massTransitStop.createMarker
Rename functions
Move `createDirectionArrow` to `MassTransitStop`
Determine arrow orientation etc. without external input
Change `create` directionArrow and marker to `get`

While at it cache creation of entities
Use cached marker MassTransitStop
Use cached direectionArrow in MassTransitStop
Move mass transit stop to dedicated module
Fix dragging of asset
Update marker position while dragging
Remove obsolete code
Remove dead code
Merge pull request #252 from finnishtransportagency/introduce-masstransitstop-as-ui-component

Introduce masstransitstop as ui component