Merge branch 'staging' into 'master'

Correct use cases

See merge request arsnova/arsnova-lite!390

docs/diagrams/use_case_diagram_frag_jetzt.puml

@@ -48,8 +48,8 @@ rectangle "frag.jetzt | use-case diagram \n" << Business >> {
     (Moderate questions) <.. (Ban question) : << extend >>
     (Evaluate questions) <.. (Ban question) : << extend >>
     (Join session) <.. (Ask question) : << extend >>
-    (Ask question) <.. (Vote down question) : << extend >>
-    (Ask question) <.. (Vote up question) : << extend >>
+    (Join session) <.. (Vote up question) : << extend >>
+    (Join session) <.. (Vote down question) : << extend >>
 
 }