add MediaType.isCompatible method

A method that compares just the type and subtype and ignores parameters. MediaType.is() could then delegate to this new method.

Same functionality as javax.ws.rs.core.MediaType:

http://docs.oracle.com/javaee/7/api/javax/ws/rs/core/MediaType.html#isCompatible(javax.ws.rs.core.MediaType)

This comparison can be done using the current api by calling withoutParameters() on both types, but this may unnecessarily allocate a new MediaType on each invocation.