Expose connected user data in wp.getOptions

To help the mobile apps help the user figure out which wp.com account
they're connected to, include user ID, username, and email in
wp.getOptions.

Also includes number of sites so the app can decide if it should suggest
Jetpack Manage.

See previous discussion in #1305
If $args are passed in to narrow wp.getOptions to one specific option, should we short circuit and not add in our additions?