notification: Add reply option to notifications for macOS.

This PR adds reply option to notifications of macOS using
`node-mac-notifier` and then post the reply for to the webapp.
It also fixes an issue that even though the app is focused the server that sent
the notification did not focus. And it also adds parsing for mentioning. This also
refactors code for notification.

Fixes: #284, #381.

app/renderer/js/components/functional-tab.js

@@ -4,7 +4,7 @@ const Tab = require(__dirname + '/../components/tab.js');
 
 class FunctionalTab extends Tab {
 	template() {
-		return `<div class="tab functional-tab">
+		return `<div class="tab functional-tab" data-tab-id="${this.props.tabIndex}">
 					<div class="server-tab-badge close-button">
 						<i class="material-icons">close</i>
 					</div>