Removed any (put|write)_file_content from the WSF_ or WGI_ OUTPUT classes

Now DEFAULT_SERVICE has to be created instead of inherited.
   - This seems to be better for new user, and this avoid potential conflict and difference when inheriting between the various DEFAULT_SERVICE implementation.
   - remember that DEFAULT_SERVICE, is mainly to help the user to build its very first service.
Use READABLE_STRING_8 as argument whenever it is possible.
Added WSF_RESPONSE_MESSAGE, and WSF_RESPONSE.put_response (a_response_message)
Now WSF_RESPONSE inherit from WGI_RESPONSE

library/server/ewsgi/specification/response/wgi_response.e

@@ -6,7 +6,7 @@ note
 deferred class
 	WGI_RESPONSE
 
-feature {WGI_SERVICE} -- Commit
+feature {WGI_RESPONSE, WGI_SERVICE} -- Commit
 
 	commit
 			-- Commit the current response
@@ -110,13 +110,6 @@ feature -- Output operation
 		deferred
 		end
 
-	write_file_content (fn: READABLE_STRING_8)
-			-- Send the content of file `fn'
-		require
-			message_writable: message_writable
-		deferred
-		end
-
 	flush
 			-- Flush if it makes sense
 		deferred