global: code restructring

* Splits demosite into a base module plus a number of
  addtional module customizations.

* Changes MAINFEST.in template to include resource files
  from new locations.

Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
deposit: article deposition

* Moves article deposition from Invenio to demosite.

* Adds missing subfield for FFT in jsonalchemy configuration.

Co-authored-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>