Wms driver client improvements

It's really huge, again... Things has moved on the openJUMP side, so I've been forced to get there here too. I've tried to improve some weakness I think their client had, I really hope they can be integrated upstream.

I've tested my work again and again... with 1.1.1, 1.1.0 and 1.3.0 WMS servers. Everything seems to run fine. There are still changes to do in OrbisGIS, particularly in the UI, in order to:
- list available styles for a layer
- be able to choose a style file
- be able to give a preferred WMS version from the UI

I think that namespace management may have to be improved too. Must dig to be sure, though.