Fixed settings dialog header; Adjust padding on dialog

Some recent changes to dialogs changed how this works and altered the look of the settings dialogs. This fixes that and makes it so that the header and content scroll independently.

Fixes https://github.com/vector-im/riot-web/issues/8329
Fixes https://github.com/vector-im/riot-web/issues/8328

src/components/structures/TabbedView.js

@@ -97,7 +97,9 @@ export class TabbedView extends React.Component {
     _renderTabPanel(tab) {
         return (
             <div className="mx_TabbedView_tabPanel" key={"mx_tabpanel_" + tab.label}>
-                {tab.body}
+                <div className='mx_TabbedView_tabPanelContent'>
+                    {tab.body}
+                </div>
             </div>
         );
     }