Moved the WMS layer name encoding to be done before the sub datasets URL...

I've moved the WMS layer name encoding from the WMS driver to the WMS Metadata set.  This shouldn't change the behaviour of the driver.

I need to tweak the sub dataset URLs (add minimum resolution, etc.) after they are created.  In the framework that I'm using, it URL encodes query parameters when building a URL.  So the sub dataset URL that I'm giving to GDAL already has the layer encoded, which results in double-encoded layer names (e.g., %20 -> %2520).