Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

* Export should always be enabled since you can export default tile set
* Fix Select All/None problem

Previously the first activeChanged signal got lost because it was not connected yet to the LinkInterface which resulted in a link incorrectly shown as inactive.

Making sure the commands are sent to the camera's actual component ID rather than a hardcoded constant.

Also distinguish Emergency Stop better

This was too confusion to expose since QGC currently does not support ArduPilot terrain tile send.

Add test for an existing window before attempting to close it.