Prepare for activation.

- Closes AC-1275.
- Flips tags and Makefile so the default build is mainnet.
- Creates a network file for mainnet.
- Sets the initial oracle to $0.50.
- Minor change to API to return remote transactions when using `<hash>@<account>`.
- Minor change to initialization to use the peer address as the external address.
- Minor change to ensure remote transactions are recorded.