Add conditional Chat/DM buttons throughout the interface

app/soapbox/features/account_timeline/components/header.js

@@ -14,6 +14,7 @@ export default class Header extends ImmutablePureComponent {
     onBlock: PropTypes.func.isRequired,
     onMention: PropTypes.func.isRequired,
     onDirect: PropTypes.func.isRequired,
+    onChat: PropTypes.func,
     onReblogToggle: PropTypes.func.isRequired,
     onReport: PropTypes.func.isRequired,
     onMute: PropTypes.func.isRequired,