Limit WKT coordinate precision to something reasonable

[kannes]

Limit coordinate precision in the filter string WKT to something reasonable. Don't always use 17 decimal places as that leads to huge filter strings and low performance when activating filters.

6 should be a good default. This is the same that GeoJSON recommends for WGS84 coordinates and usually users will use CRS with finer precision (so each decimal step corresponds with a much smaller spatial step compared to WGS84). Maybe use 7 to be safe.

Maybe add a menu/config option to set it?

[kannes]

.asWkt(precision=7) for every .asWkt()?