Display a notification when the current exit location is no longer available

From !83 (merged):

@micah: What might be better here to do would be to change the minimum to 1 exit in a country, but there should be some code in place to handle the situation where a user selects a country with one exit, and then they try to connect and that exit is no longer available, rendering their country selection no longer possible. As was mentioned in that issue, this could easily be triggered and we should guard against this by showing the user a notification that the country they selected no longer has an exit available and they would need to pick another one, or switch back to the automatic selection.