Bug 29824: Allow editing of quick spine labels

Bug 29824: Allow editing of quick spine labels

To test:
1. Apply patch
2. Go to the quick spine label tool and enter a barcode of an item with a itemcallnumber
3. Notice the 'Edit this label' button at the bottom of the page, click it
4. Edit the itemcallnumber in some way: add some line breaks, remove some, insert some new characters, remove some characters.
5. You can now print the label with your edits.

Note: This changes nothing in the database, if you relaod the same item/itemcallnumer it will have returned to its original form

Signed-off-by: Barbara Johnson <barbara.johnson@bedfordtx.gov>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>