Remove sender tooltip, and sender label, simplify MessageDelegate, add

an option to invoke GC, and update libqmatrixclient.

qml/component/DownloadDialog.qml

@@ -0,0 +1,13 @@
+import QtQuick 2.9
+import QtQuick.Controls 2.2
+import QtQuick.Dialogs 1.2
+
+FileDialog {
+    id: locationDialog
+    title: "Please choose a location"
+    folder: shortcuts.home
+    selectFolder: true
+
+    onAccepted: currentRoom.downloadFile(eventId, folder + "/" + currentRoom.fileNameToDownload(eventId))
+    onVisibleChanged: visible ? {} : locationDialog.destroy()
+}