Don't allow long-pressing on non-touchscreen devices

It isn't the right kind of interaction on a computer with a mouse or
trackpad, it should be relegated to touchscreen only. This should
hopefully cover everything from room list delegates to messages.

src/qml/AvatarTabButton.qml

@@ -34,9 +34,8 @@ Delegates.RoundedItemDelegate {
     Keys.onSpacePressed: selected()
     Keys.onEnterPressed: selected()
 
-    onPressAndHold: root.contextMenuRequested()
-
     TapHandler {
+        acceptedDevices: PointerDevice.Mouse | PointerDevice.TouchPad | PointerDevice.Stylus
         acceptedButtons: Qt.RightButton | Qt.LeftButton
         onTapped: (eventPoint, button) => {
             if (button === Qt.RightButton) {
@@ -47,6 +46,11 @@ Delegates.RoundedItemDelegate {
         }
     }
 
+    TapHandler {
+        acceptedDevices: PointerDevice.TouchScreen
+        onLongPressed: root.contextMenuRequested()
+    }
+
     contentItem: AvatarNotification {
         id: avatarNotification
         source: root.source