CWOP passcode config and action

For hams, CWOP needs a passcode other than the default -1 to accept
data.

* add a configuration setting CITIZEN_WEATHER_PASSCODE (passcode)
* passcode defaults to -1 to maintain existing behavior
* -1 may be replaced by passcode provided by CWOP server authority
* passcode is read from conf file into config structure
* apply passcode in TCP socket conversation with CWOP server