app: DEX connection notifications are spammy during registration.

[buck54321]

Especially during registration, when a connection is made and closed to retrieve the registration fee.

A partial solution would be to supress the ConnectEventFunc call when the client is shutting down cleanly, but my instinct is to not use the notification tray at all, and just rely on the disconnected icon and maybe a poke notification, and only send an error notification when the connection status prevents action.

Another partial solution is to ignore those notifications during the registration process.

[JoeGruffins]

I would like to add to this that any time a user shuts down the app they get the warning:
2020-06-08 12:16:27.787 [WRN] CORE: notify: |WARNING| (conn) DEX disconnected - DEX at 127.0.0.1:7232 has disconnected
which in this case is intended, so warning does not seem correct here.