Add PoS support

[ivanech]

When submit block fo PoS coin (I 've tried CryptogenicBullion CGB) got error:

2014-09-19 08:48:18,772 [jobmanager] [INFO] Block failed to submit to the server 127.0.0.1:8395 with submitblock! Unable to sign block, wallet locked?
2014-09-19 08:48:18,772 [jobmanager] [ERROR] {u'message': u'Unable to sign block, wallet locked?', u'code': -100}
Traceback (most recent call last):
  File "/home/vital/tmp/powerpool/powerpool/jobmanager.py", line 188, in submit_block
    res = conn.submitblock(block)
  File "/usr/local/lib/python2.7/site-packages/bitcoinrpc/authproxy.py", line 127, in __call__
    raise JSONRPCException(response['error'])
CoinRPCException: Unable to sign block, wallet locked?

The signing would be wrong because it is missing the pubkey and instead is using the address.

[icook]

Yes, there is currently no support for PoS coins with PowerPool.

[ivanech]

Do you plan to support PoS in near future?

There are only few coins with pure Scrypt/X11 etc. algo but most of coins are PoW/PoS combined.

stratum-mining written on python too, had implement PoS support over a year ago (moopless/stratum-mining-litecoin#48 and moopless/stratum-mining-litecoin@3429cb8).

[icook]

We will implement it when we need it. It may be worth noting that this software is not even 1 year old.

[eightsixeight]

how about how much would that be worth ?