[replace previous] fix for 3612 (bookseller improvements)

[replace previous] fix for 3612 (bookseller improvements)

- removing useless fields from aqbooksellers table: specialty, deliverydays,followupdays,followupscancel,nocalc, invoicedisc They were in the DB schema, but unused for years
- reworked bookseller and contract gui
- no warning thrown

NOTE : updatedatabase not done for field removal in aqbooksellers table. Should have:
ALTER TABLE `aqbooksellers`
  DROP `deliverydays`,
  DROP `followupdays`,
  DROP `followupscancel`,
  DROP `specialty`,
  DROP `nocalc`;