Update p2pool-dash for working with DashCore v0.12.1.x

[thelazier]

Please let me know if we need to add anything. Possibly version bump to compatible with DashCore release.

[thelazier]

BTW, p2pool-dash seed nodes possibly need to update, suggestions are welcome.

[thelazier]

Tested on testnet , I'm running a mainnet node (p2pool.dash.siampm.com), we still need to get in touch with other pools to update seed nodes.

[UdjinM6]

Another user confirmed successful node start with this code https://www.dash.org/forum/threads/p2pool-repository-and-python-modules-may-2016.8795/#post-113168

Probably ok to merge. @schinzelh ?

[UdjinM6]

Post-merge update:

• Confirmed by another user https://www.dash.org/forum/threads/p2pool-repository-and-python-modules-may-2016.8795/#post-113237
• 12.1 block mined by p2pool on mainnet https://explorer.dash.org/block/0000000000004f0ea4964d50b845d62893fa89138ece2cd2630b48e13ba66661