Removed redundant document keys from _view/geojson query.
Renamed one object member for more clarity.
Fixed a coding error (there was no var item=items[id]).
Used 'setOptions' to change polygon geometries.

I deem it impossible that polygon reduction would lead to a different polygon
type. That means I can just use 'setOptions' to exchange geometry (instead of
deleting and recreating a Maps Polygon).
This is presumably faster (it should be) and I don't have to store fillColor
anywhere. This property would be lost otherwise because I don't want to query
the document type twice.
Fixed wrong unified time range in _view/dimensions.