Bug 11268: increase size of biblioitems.url

Bug 11268: increase size of biblioitems.url

The URL field in biblioitems is defined as a varchar(255) which is large
enough for most URLs but not all. This patch converts it to a
TEXT field to make sure it is capable of storing all valid URLs.

Test Plan:
1) Attempt to a URL that is greater than 255 chacters long in a record
   (856$u in MARC21)
2) Save the record, note the url gets truncated
3) Apply this patch
4) Repeat step 1
5) Note the entire url is saved

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>