Add 'access' property to fields

[recidive]

In order to hide some fields or to disable filling it for some user roles, we need to add an access property to field definition.

We'll also need a mechanism for filtering out data coming from users without permissions to fill the field and to make sure we only allow altering/inserting the appropriate declared fields honoring schema definition and permissions.

[recidive]

We may also need to be able to set default values for types.