Added v-scrolling to both editors

Adds a max-height to the wiki and content editor, after which a scroll is displayed so the toolbar is accessible for editing at all times.

Changelog: changed

app/assets/stylesheets/components/content_editor.scss

 .ProseMirror {
+  max-height: 55vh;
+  overflow-y: auto;
+
   td,
   th,
   li,

app/assets/stylesheets/page_bundles/wiki.scss

@@ -152,5 +152,5 @@ ul.wiki-pages-list.content-list {
 }
 
 .wiki-form .markdown-area {
-  max-height: none;
+  max-height: 55vh;
 }