Extract MimeType as a base class of MediaType

MimeType is available in core-spring and does not include support
for quality parameters and media used in HTTP content negotiation.
The MediaType sub-class in org.springframework.http adds q-parameters.

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/RequestMappingInfoHandlerMappingTests.java

@@ -185,7 +185,7 @@ public class RequestMappingInfoHandlerMappingTests {
 			fail("HttpMediaTypeNotSupportedException expected");
 		}
 		catch (HttpMediaTypeNotSupportedException ex) {
-			assertEquals("Invalid media type \"bogus\": does not contain '/'", ex.getMessage());
+			assertEquals("Invalid mime type \"bogus\": does not contain '/'", ex.getMessage());
 		}
 	}