Add a way to cancel a connection attempt

[andrewdavidmackenzie]

When you try to connect to a remote pi, if the information is not correct or node is down or not reachable, then the UI is effectively blocked and you have to kill the app and start again.

What we should try and do is:

• not disable the cancel button when the connection attempt is started (or add another button - but "cancel" seems the obvious text for such another button)
• when the user hits the cancel button (or ESCAPE key?) send a request to cancel the connection attempt
• if there is no direct mechanism to cancel a connection attempt using the Iroh/TCP connection primities then the subscription will have to implement a timeout, or check for a cancel request periodically or some such async cancel mechanism.
• the connection attempt would stop, and the dialog would go back to previous state with the data still present and cancel button would go back to it's previous function of closing the dialog.

[andrewdavidmackenzie]

If during a connection attempt, the dialog is closed using some other mechanism (such as ESCAPE key) then catch that and also cancel the connection attempt in background, and close the dialog as the user expects.