nokia: correctly parse SMS timestamp.

The timestamp are coded on 7 BCD octets, the last one being an UTC
offset.
nokia: factor out parsing of SMS-DELIVER messages.

Additional support is implemented for Unicode messages
and Concatenated SMS.
nokia: support concatenated SMS with 16-bit reference number.
nokia: add support for alphanumeric SMS addresses.
nokia: catch a few parsing errors for better reports.
nokia: support SMS extended basic charset, type 0 addresses