Additional formats for Download like ESRI Shapefile

This pull contains commits that allows for a more generic CGI API for Up/Download: with projection and/or format transform: https://geoext-viewer.googlecode.com/svn/trunk/heron/services/readme.txt.

Also srsName is now encoded in GML. I know we are looking at native implementations for up/download, but this commit tries to finalize first the existing server/CGI-based solution.