WebSubmit: more customizable Link_Records function

* Support for linking to several records

* Unidirectional relations support

* Custom MARC fields for storing relations information

* Support for modifications of relations (using --correct
  BibUpload mode), including in records that are no longer
  linked

* Support for task sequence IDs

* Possibility to ignore failed retrieval of corresponding
  record(s)

Signed-off-by: Jerome Caffaro <jerome.caffaro@cern.ch>
WebJournal: update demo "Article Header" style

* When using "Article Header" style, create a <p> box instead
  of a <span>, to be in line with default "Sample Journal Page"
  template.

Signed-off-by: Jerome Caffaro <jerome.caffaro@cern.ch>