pidstore: refactor pidstore data model

* Moves pidREGISTRY into pid due to changes in the data model so that
  a persistent identifier has one and only one assigned object.
BibFormat: rename output format OAIDCITE to OAIDCI
BibFormat: add CC license in DataCite rights

* Adds links to CC licenses if known in the DataCite rights
  tag according to OpenAIRE guidelines.
BibFormat: add related DOIs to output

* Adds related DOIs to DataCite format template

* Adds related DOIs to HTML metadata info box
BibFormat: fix unicode decoding of user nickname
OpenAIRE: add new answers in FAQ
WebSearch: improve visibility of view button
OpenAIRE: add browse menu
BibFormat: fix tooltip text
WebSearch: remove view button from provisional

* Removes view button from provisional collections.

* Fixes an issue with button background color.
OpenAIRE: remove ZENODO user collection in index

* Removes ZENODO user collection from index overview.