First time startup wizard

[matevz]

Hackathoners always use Testnet and typically have an existing Metamask wallet to import. Let's speed up their bootstrapping time and try to teach them sth while doing so.

Add Oasis CLI start up wizard:

• Which network do you prefer?
  • Testnet (dApp developers)
  • Mainnet (other users)
• Import an existing account?
  • import an existing Ethereum-compatible or Oasis-native keypair (initiates wallet import)
  • create a new Ethereum-compatible keypair (initiates wallet create --kind secp256k1)
  • create a new Oasis-native keypair (initiates wallet create --kind ed25519)
  • none, I will manage my accounts later