Qml app: fixed import/export of plain certificate

Added TimedPopup that is a common use case so it is reusable without
  code duplication

retroshare-qml-app/src/TimedPopup.qml

@@ -0,0 +1,41 @@
+/*
+ * RetroShare Android QML App
+ * Copyright (C) 2017  Gioacchino Mazzurco <gio@eigenlab.org>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+import QtQuick 2.7
+import QtQuick.Controls 2.0
+
+Popup
+{
+	property alias duration: timer.interval
+
+
+	id: popupRoot
+	visible: false
+	onVisibleChanged: if(visible) timer.start()
+	x: parent.x + parent.width/2 - width/2
+	y: parent.y + parent.height/2 - height/2
+
+
+	Timer
+	{
+		id: timer
+		interval: 1500
+		onTriggered: popupRoot.close()
+	}
+}
+