Test if work key is present

When creating a new work and associating the reproduction, the work id
may not yet be initialized when the __unicode__ method is called (for
logging element change). So check beforehand for the existence of work.
Add missing reference indirection
Add link to bibliography
Fix typo
Define default ordering for ExhibitionInstance
Add title in exhibition admin form
Increase thumbnail size to 240x240
Modify help text
Specify ordering for all classes
Fix image positioning when there are multiple associated images
Add update_pivot script
Add safety test

This condition can happen when the solr index is out of date. In this
case, degrade gracefully instead of plainly break.
Fix multi-image frame behaviour
Load local settings from local_settings file
Add reference for inplace editing libs
Allow null price values
Allow blank owner fields
Remove publication_date and page_number from search_fields
Preferably use abreviation to title for a bibliography reference
Rename "En groupe"  to "Groupe"