vtkMap should register layers when they are added.
vtkFeatureLayer should register features it adds
vtkGeoJSONMapFeature should register PolyData, also delete InputString
vtkOsmLayer should delete cached tiles
Remove memory leaks from qtWeatherStations class
Fix *big* memory leak introduced during vtkOsmLayer refactor

Was adding same map tile twice
Occurred sometime before commit 6149e4c6 (26-Oct-2014)
Fix issues in multithreaded layer, exposed by memory leak fixes.
More memory leak fixes
Replace shallow copy with register call
Don't need to explicitly delete MapWidget, since it's owned by qtMapFrame
Merge pull request #70 from OpenGeoscience/john/object-lifecycle-fixes

John/object lifecycle fixes