cds: use the OAI-PMH spider to harvest CDS

[szymonlopaciuk]

Supersedes #198.

Description

This uses the OAI-PMH spider to harvest CDS. Drops HarvestingKit dependency from the CDS spider as inspirehep/inspire-dojson#165 added support do harvest CDS directly.

Related Issue

Fixes #199.

Checklist:

• I have all the information that I need (if not, move to RFC and look for it).
• I linked the related issue(s) in the corresponding commit logs.
• I wrote good commit log messages.
• My code follows the code style of this project.
• I've added any new docs if API/utils methods were added.
• I have updated the existing documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[michamos]

Superseded by #259.