Use message mixin for handling success and error messages (#51)

Use message mixin everywhere

Add mixin for success and error messages

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/frontend/pulls/51

src/message/index.js

@@ -40,5 +40,4 @@ export default {
 
 		context.loading = false
     },
-
 }