BibSched: Tasklet + bfe for PDF icon creation

* Added tasklet that will create icons for all BibDocs without an
  icon.

* Added BibFormat Element BFE_ICON that will display the icon on
  HTML brief format.
BibFormat: prevent display of empty Altmetric

* Added tasklet to download and store Altmetric id in 035__a/9

* Changed BFE_OPENAIRE_ALTMETRIC to only show badge if an altmetric id
  exists in 035__a, thus preventing "question mark"-badges to show up.
OpenAIRE: fix spelling