deposit: Importer class for import

* Can import from multiple sources.

* Makes the queries in parallel.

* Combines the queries results in a configurable
  way.

* Fixes authors contributors mapping when no
  extract_contributors function defined in a
  Filter object.

Signed-off-by: Kamil Neczaj <kamil.neczaj@cern.ch>
deposit: MessageBox jQuery plugin

* Converts a DOM object to a container showing
  messages with given Hogan template.

Signed-off-by: Kamil Neczaj <kamil.neczaj@cern.ch>