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

cleanup.

qml/component/FileBubble.qml

@@ -0,0 +1,22 @@
+import QtQuick 2.11
+import QtQuick.Controls 2.4
+import QtQuick.Controls.Material 2.4
+
+AvatarContainer {
+    DownloadableContent {
+        id: downloadable
+
+        width: downloadButton.width
+        height: downloadButton.height
+
+        Button {
+            id: downloadButton
+
+            text: content.body
+
+            highlighted: !sentByMe
+
+            onClicked: downloadable.downloadAndOpen()
+        }
+    }
+}