Enhance implementation of Abstract test A.6

[dstenger]

Currently, only the first test method of the abstract test is implemented.

The second test method is missing:
"2. Validate that the content of that response is consistent with the format requested via HTTP content negotiation and represents elements inside or intersecting with the spatial extent of the geographical area of the tile identified by the tile matrix, tile row and tile column of the tileset’s tile matrix set." (copied from spec with id 20-057)