Add externally open image support & file download support && more code

cleanup.

qml/component/DownloadableContent.qml

@@ -0,0 +1,35 @@
+import QtQuick 2.11
+import QtQuick.Controls 2.4
+
+Item {
+    width: parent.width
+    height: visible ? childrenRect.height : 0
+
+    property bool openOnFinished: false
+    readonly property bool downloaded: progressInfo && progressInfo.completed
+
+    onDownloadedChanged: {
+        if (downloaded && openOnFinished)
+            openSavedFile()
+    }
+
+    function downloadAndOpen()
+    {
+        if (downloaded)
+            openSavedFile()
+        else
+        {
+            openOnFinished = true
+            currentRoom.downloadFile(eventId)
+        }
+    }
+
+    function openSavedFile()
+    {
+        if (Qt.openUrlExternally(progressInfo.localPath))
+            return;
+
+        if (Qt.openUrlExternally(progressInfo.localDir))
+            return;
+    }
+}