Added means to fetch user's Google profile
Added means to fetch user's Google profile

The existing GoogleEmail2 auth did that:
  - Acquire user access token with offline access
  - Use token to acquire user's profile
  - Build `Creds` with user's email as `ident` and the other profile
    details as stringy key-value pairs in `credsExtra`

This wasn't enough for me, for several reasons:
  - Access token was not saved after authentication. If we request 'offline'
    token why not to have a way of using it later.
  - Stringy key-value profile is not nice and `credsExtra` can be accessed
    only from `getAuthId`
  - I might want to request the profile after authentication process

So I've added the needed features.
  - The access token is saved in a session
  - There is a `Person` type with `FromJSON` instance and `getPerson`
    can be used to acquire it from `HandlerT`

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