At least the BE and the NL DSMR devices use MBUS.
Therefor we make the MBUS obis reference generic, and convert the V5
telegram to use MBUS values.
Also remove BELGIUM_MAX_POWER_PER_PHASE as this was a duplicate.
Finally set self.maxDiff = None to have a full test output on some
tests.
* issue-51-telegram improved mbus device parsing; refactored TelegramParser.parse to return Telegram object which is backwards compatible with the dict result
Sometimes the timestamp in the DSMR message is invalid (when no data
read read from the mbus meter?), and then parsing fails.
Fixing this by handling the exception and returning None for invalid
timestamps. Fixes: #120
