handle JTS geometries that are null or empty correctly and do not check lon and lat of Coordinates supporting also metric CRS

#28 by mistake reverted #27 and #26 

1) JtsAdapterFactory and JtsAdapterFactoryTest: handle JTS geometries that are null or empty correctly (i.e contain no coordinates) correctly (same idea as in lurajon@877b13c )

2) Coordinates and CoordinatesTest: do not check lon and lat parameters in constructor of Coordinates supporting also metric CRS (Coordinate Reference Systems):

define lon and lat like in OpenLayers (see constructor http://dev.openlayers.org/releases/OpenLayers-2.13.1/doc/apidocs/files/OpenLayers/BaseTypes/LonLat-js.html )
allowing alternative map units (kilometer, meter, mile, foot and inch) additional to degree
(idea from http://dev.openlayers.org/releases/OpenLayers-2.13.1/doc/apidocs/files/OpenLayers/Map-js.html#OpenLayers.Map.units )

Good it was probably out of the scope for a serialization lib.