OAIHarvest: fix admin pages

* Fixes broken imports in admin pages of OAI harvest sources.
  (closes #2188)

* Bootstraps some templates for easier human interaction.

* Uses the oaiharvester.models.OaiHARVEST for interacting with DB.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>