MMS defines several status groups. They may have errors of the same
meaning but assigned with different numbers. Rename error value
constants to prevent from name collisions.
Also simplify decoding process.
* Document Address.decode()
* Merge CharsetEncodedString into EncodedStringValue
* Merge ClassIdentifier into MessageClassValue
* Export missed coder objects and fix test scripts as well
* ReplyChargingValue is defined in MmsPduHelper, not WspPduHelper
* Fix multiple decode test cases data
* Char-set value in EncodedStringValue should be decoded as IntegerValue
* Don't insert per PDU typeinfo into decoded MMS message object
* "Date" is also a mandatory field for M-Retrieve.req PDU.
