[web3-react] Simplify connect context

[polarker]

All changes to the ConnectContext would trigger rerender, so we should keep the global context as simple as possible. The following should be removed and devs should use other hooks useAccount and useBalance etc.

  account?: Account
  setAccount: React.Dispatch<React.SetStateAction<Account | undefined>>
  displayAccount?: (account: Account) => string
  signerProvider?: SignerProvider
  setSignerProvider: React.Dispatch<React.SetStateAction<SignerProvider | undefined>>
  addressGroup?: number
  keyType?: KeyType
  network?: NetworkId

[Elite-tch]

I'd love to give this a go.