Add throwExceptionIfNoHandlerFound property

Add a property to customize if an exception should be thrown when no
handler was found to process a given request.

Closes gh-4000

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -151,6 +151,7 @@ content into your application; rather pick only the properties that you need.
 	spring.mvc.favicon.enabled=true
 	spring.mvc.message-codes-resolver-format= # PREFIX_ERROR_CODE / POSTFIX_ERROR_CODE
 	spring.mvc.ignore-default-model-on-redirect=true # if the content of the "default" model should be ignored redirects
+	spring.mvc.throw-exception-if-no-handler-found=false # if a "NoHandlerFoundException" should be thrown if no Handler was found to process a request
 	spring.mvc.async.request-timeout= # async request timeout in milliseconds
 	spring.mvc.view.prefix= # MVC view prefix
 	spring.mvc.view.suffix= # ... and suffix