Changed the db structure: Added 2 tables literature_links, literature_links_temp and deleted the link fields from the literature_lit(_temp) tables.
Literature dbobject refactored: member linktoread => links, links => refs
Added a data model for the links
Added the new link dbobject to the literature dbobject
Marc21 and Pica+ parser adjusted and refactored. Multi links are now supported. Untested.
Added cron taks for deleting the temp links of the search results. Adjusted the function which inserts the search results into the db, has now multi link support.
Bugfixes in Pica+ parser, Search results can now save and dislay links properly.
Added and tested link support for everything except the import/export modules.
Added a ISBN fix for lazy bib people which store multiple isbns in the same field