global: item revision endpoint

[mvesper]

• Adds the endpoint configuration for Item.find_by_holding.

[mvesper]

Things to consider:

• If we just create a Search class, we kinda have to mimick some of the elasticsearch_dsl behavior.
• Do we want to create our own queryparser for this? Right now I just deconstruct elasticsearch_dsl objects.
• The CIRCULATION_REST_ENDPOINT config is a bit 'dirty', since I defined a pid_type that doesn't exist and that I don't need. But maybe there is a neither way to go for it.

[egabancho]

LGTM

[david-caro]

Looks good to me :)

[mvesper]

@jirikuncar Changed the copyrights :)

[jirikuncar]

@mvesper you should just add 2017 and keep 2016.

[mvesper]

@jirikuncar x) fixed