Filter out ExtendedCapabilities when reading WebMapTileService

[geographika]

Fix for #965.

Tested with the following:

from owslib.wmts import WebMapTileService
service_url = "https://api.dataforsyningen.dk/dhm_bluespot_ekstremregn?token=f3ecb52320902f733a433aa9945d8dc8&"
wmts = WebMapTileService(service_url)

tile = wmts.gettile(layer='bluespot_ekstremregn_0',
                    tilematrixset='View1', tilematrix='L00',
                    row=0, column=0, format="image/png")
print(tile.info()['Content-Type'])

# without fix - AttributeError: 'OperationsMetadata' object has no attribute 'name'

CC @CJGutz - can you check if this fixes it for you.

I'm considering adding a "live" test for this pointing to https://api.dataforsyningen.dk but endless test failures due to service changes are a concern. Long-term it may be better to spin up a local test server and return local XML and other files.

[CJGutz]

Yes, this works for me. Thank you!