base: folder refactoring

* Moves fixtures and data from base/ to demosite/ folder.

* Updates README accordingly.

Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>
base: port old KBs to overlay

* Creates new knowledgeext/kb/ folder where all KB files
  are stored.

* Creates fixture classes on the fly based on KB file
  content.

* NOTE Using $ inveniomanage database recreate
  will load all KBs into the database which is a one-off slow process.

Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>
base: new Subjects KB

* Adds Subjects KB (used by deposit form).

* KB loading small enhancement to support matching of kb files
  independently of capitalization.

Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>
config: add CELERY_ACCEPT_CONTENT

* Adds the config variable CELERY_ACCEPT_CONTENT in order to
  specify the only accepted content for Celery workers.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
deposit: form fields show/hide enhancements

* Removes collaboration box.

* Hides parent boxes with specific class.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
Co-authored-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>