Add feedback to MapVisualizer inspector to help configure properly

[david-rhodes]

Warn user if a TerrainFactory is missing, as this is needed to render the raster results.

[brnkhy]

You don't have to have a TerrainFactory though. Remember contour line demo or a Godus style terrain wouldn't have it (they ar ejust mesh factory as contour lines are in vector data).

[david-rhodes]

@brnkhy I suppose I meant if you add a MapImageFactory, then we should warn that terrain is also needed, even if only FlatTerrain.

[brnkhy]

@david-rhodes ah alright that makes sense.

[david-rhodes]

Not super important.