Lightwalletd mainnet/testnet compatibility

[braddmiller]

Story: As a wallet developer I would like a block server that allows me to quickly switch connection between mainnet and testnet so that I can test and deploy quickly.

Criteria:

1. Connection to either chain is as simple as passing a parameter
2. After initial sync, reconnecting to either network only requires syncing from the last known block
3. It is clear to any client connecting to the server which network it is connected to

Assigned to: Larry
Points: 8

[LarryRuane]

This can be considered low priority.