Add multi-pubkey return support for the authorize method

[sdlaver]

Spec

• Update sign_and_send_transactions, sign_transactions, and sign_messages to accept an account param.

Fakewallet

• Allow user to choose addresses to share with the dApp during authorize

JavaScript protocol

• Augment signMessages to accept addresses param
  Thread the currently selected address through to each signMessages call #176

• Augment signTransactions to accept address param Now inferred from transaction.
• Augment signAndSendTransactions to accept address param Now inferred from transaction.

React Native Example App

• Show dropdown selector when more than one pubkey
  Offer menu to select address when more than one are authorized (React Native app) #173
• Update calls to protocol API to specify the address that should sign
  Thread the currently selected address through to each signMessages call #176

JavaScript wallet-adapter-mobile plugin

• Offer way for dApps to inject an address chooser method
  feat: you can now configure the SolanaMobileWalletAdapter with an address selector #171

Mobile web example app

• Use address chooser to present an address selection UI to users