Additional mediatype constants

[johnlcox]

JAX-RS includes a MediaType class which has constants for most of the common HTTP media types.

With the addition of the @PATCH method annotation it may be desired to start using either of the two common JSON PATCH media types for implementations.

In my mind there are two options.

1. A single class for all additional media types. Something like AdditionalMediaTypes with constants like APPLICATION_MERGE_PATCH_JSON and APPLICATION_JSON_PATCH_JSON.
2. Classes that provide additional context around what media types they have constants for. Something like PatchMediaTypes with constants named similarly to above.

Another question we should think about is how will we decide which media types to include in beadledom?