Provide meta data for list requests

[arueckauer]

List responses contain meta data information (per_page, total_pages, total_entries and so forth) which are currently not accessible, since a collection object with no further information is returned.

See for example List all users.

{
 // [..]
 "per_page":100,
  "total_pages":1,
  "total_entries":3,
  "next_page":null,
  "previous_page":null,
  "page":1,
  "links":{
    "first":"https://api.harvestapp.com/v2/users?page=1&per_page=100",
    "next":null,
    "previous":null,
    "last":"https://api.harvestapp.com/v2/users?page=1&per_page=100"
  }
}