Fixes for 1.12 (#4655)

* fix missing locales
* bump composer packages
* changed translations
* assert timezone on customer
* include user accountNumber in excel export
* improve next customer number calculation
* fix z-index of contextmenu / action dropdown

assets/sass/tables.scss

@@ -153,3 +153,10 @@ table.table-hover {
         }
     }
 }
+
+/* For the context menu */
+.action-dropdown,
+.actions .dropdown .dropdown-menu {
+    // stay on top of sticky elements (like table header)
+    z-index: 1021;
+}