clean up network descriptions
Added chain ID for Namecoin.

AuxPoW support now depends on presence of an AuxPoW chain ID, rather than being Namecoin-specific. This enables support for Dogecoin AuxPoW.
Add Dogecoin test cases

Added test cases covering Dogecoin address validation, block parsing, merkle root calculations
and full AuxPoW block validation.
Handle empty merkle branches

Corrects the issue where calculating merkle root from an empty merkle branch results in
nil. Now correctly returns the original hash.
fix block notifications on reorg
Merge remote-tracking branch 'upstream/master'