Updating mimetype accept header parsing to use builtin aspnet parse/methods

[Banashek]

Fixes 485

This change updates the mustAccept to base it's decisions on the values of parsed MediaTypeHeaderValue values instead of strings.

It utilizes the isSubsetOf method of that class in order to do proper subset matching.

While the parsing is wrapped in an exception handler during the runtime execution, the construction of the function does not wrap the parsing. This is so that it will fail fast on startup (developer supplied values), but tolerate malformed values at runtime (bad user input).

I've added only a couple of tests, but believe it should suffice for this scenario since the code leans on the Net builtins.

Happy to make changes (remove rfc comments, etc) if desired.

[baronfel]

👍 I like this approach a lot! Build failures are due to package versions being integers instead of semver versions, as I think you've mentioned in another issue

[dustinmoris]

LGTM, many thanks!