BibSched: icons creation tasklet

* Tasklet to create icons of the files attached to a record.

Signed-off-by: Ludmila Marian <ludmila.marian@cern.ch>
Acked-by: Jerome Caffaro <jerome.caffaro@cern.ch>
BibSched: more customizable icon creation tasklet

* Added parameter 'icon_format_mappings' to define the format
  of the created icons for each source file format.
  Defaults to newly introduced CFG_ICON_CREATION_FORMAT_MAPPINGS.

* Added parameter 'docnames' to choose for which BibDoc the icons
  should be created

* Added parameter 'add_default_icon' to mimic the traditional
  behaviour of WebSubmit when adding default gif icon.

* Added parameter 'inherit_moreinfo' for created icons to inherit
  the comment and description values of the source BibDoc.

Signed-off-by: Jerome Caffaro <jerome.caffaro@cern.ch>
Acked-by: Ludmila Marian <ludmila.marian@cern.ch>
BibDocFile: convert files and icons asynchronously

* When uploading files via the document file manager interface,
  do not attempt at creating other formats and icons immediately,
  but delay their creation via the use of dedicated tasklets, in
  order to reduce the waiting time on the user's side.
  (closes #1428)

* Introduces parameter 'deferRelatedFormatsCreation' in
  Create_Upload_Files_Interface WebSubmit function to fall back
  to previous behaviour if "related formats" creation should
  happen immediately.

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