Add --testnet and --mainnet flags
Add --testnet and --mainnet flags

Error if both are specified.

oktapodia/decrediton-appveyor-test,decred/decrediton,decred/decrediton,oktapodia/decrediton-appveyor-test,decred/decrediton,decred/decrediton,oktapodia/decrediton-appveyor-test,oktapodia/decrediton-appveyor-test,oktapodia/decrediton-appveyor-test,decred/decrediton,decred/decrediton