Mapfishapp osm ogr

This adds the support of OSM files into Mapfishapp ("add a new layer by sending a file")

OSM files can be generated using overpass-api (see http://www.overpass-turbo.eu/), via JOSM, using a plain planet file (but you don't plan to send some gigabytes of dumped data to a web application ?), ...

For now on, the OGR implementation of OSM format is used, there is no pure java (GeoTools) implementation, so it requires a mapfishapp nested into a tomcat correctly configured (with native libs).

I don't know if the OSM file format is a must for spatial data infrastructures, but at least, this PR is a PoC showing that adding OGR-supported file formats is somewhat simple.

TODO: document a little bit more.