timeline: Load avatars asynchronously

Speeds up scrolling through the timeline.

src/timeline/AvatarFlow.qml

@@ -28,6 +28,7 @@ Flow {
             name: displayName
             source: avatarUrl
             color: memberColor
+            asynchronous: true
         }
     }
     QQC2.Label {

src/timeline/HiddenDelegate.qml

@@ -49,6 +49,7 @@ TimelineDelegate {
                 name: root.author.displayName
                 source: root.author.avatarUrl
                 color: root.author.color
+                asynchronous: true
             }
             QQC2.Label {
                 Layout.fillWidth: true

src/timeline/MessageDelegate.qml

@@ -250,6 +250,7 @@ TimelineDelegate {
                 name: root.author.displayName
                 source: root.author.avatarUrl
                 color: root.author.color
+                asynchronous: true
                 QQC2.ToolTip.text: root.author.htmlSafeDisambiguatedName
 
                 onClicked: RoomManager.resolveResource(root.author.uri)

src/timeline/ReplyAuthorComponent.qml

@@ -40,6 +40,7 @@ RowLayout {
         source: root.author.avatarUrl
         name: root.author.displayName
         color: root.author.color
+        asynchronous: true
     }
     QQC2.Label {
         id: replyName

src/timeline/StateComponent.qml

@@ -49,6 +49,7 @@ RowLayout {
         source: root.author?.avatarUrl ?? ""
         name: root.author?.displayName ?? ""
         color: root.author?.color ?? Kirigami.Theme.highlightColor
+        asynchronous: true
 
         MouseArea {
             anchors.fill: parent

src/timeline/StateDelegate.qml

@@ -105,6 +105,7 @@ TimelineDelegate {
                             name: parent.modelData.displayName
                             source: parent.modelData.avatarUrl
                             color: parent.modelData.color
+                            asynchronous: true
                         }
                     }
                 }

src/timeline/TimelineEndDelegate.qml

@@ -36,6 +36,7 @@ TimelineDelegate {
 
                 name: root.room ? root.room.displayName : ""
                 source: root.room ? root.room.avatarMediaUrl : ""
+                asynchronous: true
 
                 Rectangle {
                     visible: room.usesEncryption