This reverts 4d619d71b1 (see #1527), going back to what we had after e13075f6ff (see #881).
To avoid the 404 in the hosted examples, the css is copied to the same relative path when hosted as during development.
This allows us to cast single-part geometries to multi-part types before adding features to the target layer. This doesn't yet allow for drawing multi-part geometries with multiple parts. That can be handled separately.