Use a custom class that extends from OL.Layer.WMS for the map layers

[Glodenox]

Instead of trying to shoehorn the necessary functionality in from the outside of the OpenLayers.Layer.WMS class, it would make a lot more sense to inherit from the object and add a bunch of the functionality in there.

This would definitely make the tile manipulation a lot less demanding as we can just use canvas elements instead of imgs. It would also make retrieving the error messages possible directly instead of having to call the service again, which would allow the removal of all @connect headers added in #12. And on top of that, it would also allow for a clean solution for the issues encountered in #23 as Proj4js possibly wouldn't need to be exposed to the rest of OpenLayers for it to work.

This would be a major refactoring for the better.