GeoJSON defaults to WGS84 if no CRS is defined (according to spec).
Moved extraction of the EPSG integer into utils/EPSG(GeoJSON).

Actually there's only named and linked CRS'es but it makes more sense to have
the functionality in one place.
Changed 'error' crs to match the GeoJSON scheme more closely.
Changed _view/geojson to emit source EPSG.

The EPSG is included only if no simplification was done.
Changed utils/EPSG() to return WGS84 if no CRS is defined.
Changed utils/simplify() to correctly identify WGS84.

The catch/throw blocks have never been my favourite, so good work so far, me!!!
Changed comment to reflect it being a sentence.
Implemented EPSG as a query parameter to _list/export.

The parameter I'll probably never use, but I let it default to the first EPSG
of all geometries. In this case, coordinates are offset only by about 2mm and
that is close enough for me.
The projection definitions are terrible and need review, none the less.