OpenAIRE: upload usability report improvements

* UI improvements based on usability assesment.

* Adds improvements in difference between save and
  submit as well as additional help text to explain
  that edits are not possible after submission.

* Adds UI reposnse on save for both top and bottom

* Fixes issue with communication error being report
  as warning instead of error/danger.
OpenAIRE: fix selected form collections display

* Fixes an issue with saved collections not being displayed after
  a reload.
WebStyle: fix menu css issues

* Fixes issue with color of carets and links when overing over menus
  and dropdown.
global: rename user collections to communities
OpenAIRE: remove and redefine some collections

* Redefines some collections to use 980__a instead of 980.

* Removes collections curated and uncurated.
pidstore: initial release

* Implementation of persistent identifier store for managing
  registration of persistent identifiers for Invenio objects.
OpenAIRE: reserve doi feature in upload form

* Adds a button to pre-reserve a DOI prior to the final submit.
OpenAIRE: remove print statements
BibFormat: fixed issue with subjects-tag

* Fixes an issue where if no keywords where defined an
  empty subjects-tag would be added which DataCite could not
  validate.
OpenAIRE: add registration of DOI through DataCite

* Adds a Celery task which will register an ZENODO DOI.