Associate Publication with multiple Groups, additional filters

New Features:

• multiple working groups can be assigned to a publication
• working groups are not shown in main table anymore
• working groups are listed on publication view page with Icon + working group name
• the search function allows multi-term-search by quotation marks (text between two quotation marks is seen as one search term), multiple search terms are still searched via 'or' condition
• external IDs were added to the Excel export
• publications can be filtered by working groups and external IDs (individually or jointly)
• a button was added to show all publications without pager
• default ordering changed to publication year (descending)