Rewrite FileDialog in C++ && add setting to force async load timelime.

Also fixes repeat section label and empty space when message is redacted.

Fixes #27

qml/component/DownloadDialog.qml

@@ -1,13 +0,0 @@
-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()
-}

qml/component/DownloadableContent.qml

@@ -17,7 +17,7 @@ Item {
     onDownloadedChanged: downloaded && openOnFinished ? openSavedFile() : {}
 
     function saveFileAs() {
-        Qt.createComponent("DownloadDialog.qml").createObject(this).open()
+        matriqueController.saveFileAs(currentRoom, eventId)
     }
 
     function downloadAndOpen()

qml/component/MessageDelegate.qml

@@ -4,7 +4,7 @@ import QtQuick.Controls.Material 2.2
 import Matrique 0.1
 
 Item {
-    id: messageDelegate
+    readonly property bool hidden: marks === EventStatus.Redacted || marks === EventStatus.Hidden
 
     readonly property bool darkTheme: Material.theme == Material.Dark
     readonly property color background: darkTheme ? "#242424" : "lightgrey"
@@ -12,7 +12,7 @@ Item {
     readonly property bool sentByMe: author === currentRoom.localUser
     readonly property bool isState: eventType === "state" || eventType === "emote"
 
-    visible: marks !== EventStatus.Hidden
+    id: messageDelegate
 
     z: -5
     width: delegateLoader.width
@@ -29,8 +29,10 @@ Item {
     Loader {
         id: delegateLoader
 
+        asynchronous: setting.asyncMessageDelegate
+
         source: {
-            if (eventType == "redaction") return ""
+            if (eventType == "redaction" || hidden) return ""
             switch (eventType) {
             case "state":
             case "emote":