492/antiquarian bibliographic work

[tcouch]

closes #492

• Updates the Work model with a bibliographic boolean flag.
• As per unknown works, an Antiquarian on save signal triggers a check to see if it has a bibliographic work and creates one if not
• Also checks for duplicate biographical works and combines them into one if so (shouldn't happen anyway)
• Fixes bug spotted in unknown work's remove duplicates method which would have stolen links from other, non-unknown works
• Incorporates bibliographic work into ordering logic so it is always the second to last work before unknown
• Updates/fixes the detail template so it does not appear reorderable
• Migration includes a step to add an empty biographical work to all existing Antiquarians