InboxPage: use sparse fields to improve query performance

[Gnito]

NOTE: If you have changed InboxPage component, check if any data is missing. This deliberately drops some of the fields of Transaction and user entities away from the template.

This improves InboxPage performance a bit by reducing the amount of fetched data. It also serves as an example of how to use sparse fields:

    'fields.transaction': [
      'lastTransition',
      'lastTransitionedAt',
      'transitions',
      'payinTotal',
      'payoutTotal',
    ],
    'fields.user': ['profile.displayName', 'profile.abbreviatedName'],

Currently, TransactionPage doesn't use data loaded on InboxPage. So, we can expect that there is no partially loaded data when TransactionPage is rendered.
(So, this differs from navigating from SearchPage to ListingPage.)