No longer do our `mainnet` and `testnet` buttons set specific RPC urls. Now they set `provider.type`, which gets interpreted with code.
Currently the provider types of `mainnet` and `testnet` point to our new scalable backends, but these could be re-interpreted to use any other provider, be it etherscan, peer to peer, or otherwise.
Makes it easier for us to upgrade our infrastructure without incorporating migration logic into the program.