Runtime validation cases

[murithigeo]

1. Arguments: No need to specify that document is a URL via the source=url flag. Remember to use absolute URLs with scheme
2. NdArray: axisNames,shape, tileShape contains valid lengths and arrangement. Does not check for edge tiles though. Ranges also reference existing parameters
3. Validate that the dataType and axisNames from a loaded TileSet are the same as those of parent TiledNdArray
4. categoryEncoding: If specified, then the member categories is expected in the observedProperty
5. TiledNdArray: Validate that urlTemplate is valid (variables are of tiled axisNames).
6. media type: If an URL is passed, then expect the response to have the correct content-type header. If it is application/prs.coverage+json, warn of the deprecation, else warn of the incorrect header value
7. categoryEncoding: If specified, values of categories are unique. Because of the approach, expect that values of ranges are integers
8. categoryEncoding: If specified, then the values of the NdArray's should only include those in categoryEncoding
9. Add tests to validate the runtime_validator
10. Add sanity checks for the runtime_validator
11. ParameterGroup: elements of members reference existing parameters

This MR partially addresses #opengeospatial/CoverageJSON#179
This validation approach fetches all variations of a TiledNdArray and recursively tests resulting ranges thus increasing validation time

[jonblower]

Must admit that I haven't reviewed the code in detail but it looks reasonable and the tests behave as expected. Many thanks for this important contribution!