BibCirculation: arrival date and library merge
- Added column 'expected_arrival_date' in crcITEM
- Made this field modificable in 'update_item'
- 'expected_arrival_date' displayed in the status column (only if the status is 'on order')
- Added functionality to merge 2 libraries.
- Items and requests for library1 are assigned to library2 and library1 is deleted.