Projection discovery system

[GoogleCodeExporter]

The Google projection used in the AtlasMapper is the un-official EPSG:900913. 
It is well supported by GeoServer but not supported by ncWMS.

The official Mercator projection (EPSG:3857) is known to be supported by the 
latest ncWMS version, but not well supported with old version of GeoServer.

A projection discovery system is needed to know which projection each data 
sources support. Than, when selecting the client's data sources, grey out the 
one that the client do not support. Also, a projection aliases system is needed 
to know that all Mercator projection are equivalent, so a data source 
supporting EPSG:900913 can be added to a client using EPSG:3857.

See: http://wiki.openstreetmap.org/wiki/EPSG:3857

Original issue reported on code.google.com by [email protected] on 15 Jul 2013 at 11:39