This is the first part of the API. It supports most of contacts, as well as the
journal. This PR also brings Monica to Laravel 5.5, as the API required it with
the new concept of resources. It needs to run `php artisan migrate` as well as
`php artisan passport:keys` to generate the access tokens needed for the API.
* Edit relation docblocks of Contact model
* Move activities to its own controller
* Move reminders to its own controller
* Move tasks to its own controller
* Refactor Gift in preparation for the move
* Move gifts into its own controller
* Fix failing tests
* Move debt to its own controllelr
* Fix tests failing on PHP7
* Move significant others to its own controller
* Move kids to its own controller
* Move notes to its own controller
* Some more adjustments & solving #277
And more query optimizations
