feature: Add DND button in left sidebar.

This adds the do not disturb button to the left sidebar
which disables sound and notifications. It also disables
flash taskbar on windows.

Fixes: #298.

app/renderer/js/utils/dnd-util.js

@@ -0,0 +1,41 @@
+'use strict';
+
+const ConfigUtil = require(__dirname + '/config-util.js');
+
+function toggle() {
+	const dnd = !ConfigUtil.getConfigItem('dnd', false);
+	const dndSettingList = ['showNotification', 'silent'];
+	if (process.platform === 'win32') {
+		dndSettingList.push('flashTaskbarOnMessage');
+	}
+
+	let newSettings;
+	if (dnd) {
+		const oldSettings = {};
+		newSettings = {};
+
+		// Iterate through the dndSettingList.
+		for (const settingName of dndSettingList) {
+			// Store the current value of setting.
+			oldSettings[settingName] = ConfigUtil.getConfigItem(settingName);
+			// New value of setting.
+			newSettings[settingName] = (settingName === 'silent');
+		}
+
+		// Store old value in oldSettings.
+		ConfigUtil.setConfigItem('dndPreviousSettings', oldSettings);
+	} else {
+		newSettings = ConfigUtil.getConfigItem('dndPreviousSettings');
+	}
+
+	for (const settingName of dndSettingList) {
+		ConfigUtil.setConfigItem(settingName, newSettings[settingName]);
+	}
+
+	ConfigUtil.setConfigItem('dnd', dnd);
+	return {dnd, newSettings};
+}
+
+module.exports = {
+	toggle
+};