Initiate connection to Metamask wallet

[dnaidionov]

If user isn't connected to their Metamask we shall display a welcome screen with a CTA "Access My MetaMask Wallet". Upon clicking CTA we display a modal with T&C acceptance confirmation (like on myetherwallet). If user agrees, we initiate a connection to Metamask and read user's account. We should be able to get a list of all addresses in the user's wallet, and display ETH and token balances as cards (see #TBA)

Prototype/sketch file: TBA