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.
This normalizes all relationships and adds relations to models to take advantage of laravel's eagerloading and reduce queries to the database.
This might go against the 'add any kind of complexities whatsoever' rule in the contribution guide, but I think adding relations would eventually simplify the code base. The amount of queries just on the dashboard fell from ~70 to 26. There's also a lot of boilerplate code in the Contact model to retrieve relationships and to maintain accurate count of them (fields like number_of_*). They can be greatly simplified with the addition of relations.
One other thing in the Contact model was the definition of the Contact-User relation. This definition uses the account_id field in the contacts table and and relates it to id in users. I'm not sure if this is the intention, since the id from accounts table is used when assigning account_id for a contact. This seems to have worked so far, because both a user and its associated account are created at the same time during registration and their ids match, but if there was any difference, this relationship would relate wrong contacts and users. I changed the relationship name to account. This makes the path to a user from a contact is $contact->account->user right now.
