Turn "fast bbox" into a datastore hint

Fast bbox is a nice option allowing to choose between speed of test and accuracty. We enable it by default to allow for fast WMS responses (where accuracy is not needed) but this means we have less accurate GetFeature responses. There is no need to make the user have to choose between one or the other, if we turn fast bbox into a query hint we can have both: WMS can set fast bbox hint in their queries, whilst WFS won't and will use accurate intersection checks.