Bug 11368: Add script to import Lexile scores

Bug 11368: Add script to import Lexile scores

Koha needs a script to automate the importing of Lexile score data for
titles that have available scores but are not currently in the title's
record.

This script will take a CSV file of Lexile scores, and locate any
matching records in the Koha database ( by ISBN ). If the record already
has a score, it will be updated. If not, the Lexile score field will be
created.

Test Plan:
1) Apply this patch
2) Catalog a record for each of the following ISBNs:
   0789170191
   9780673779410
3) Download the file LexileTitlesTruncated.txt attached
   to this bug report
4) Run the script from the command line:
   ./misc/migraction_tools/import_lexile.pl -v --file /path/to/LexileTitlesTruncated.txt
5) View those records in Koha
6) Note those records now have valid Lexile scores
7) Edit the Lexile score ( 521$a ) and change the value to something else
8) Repeat step 4
9) Note the original Lexile score has been restored

Signed-off-by: Mirko Tietgen <mirko@abunchofthings.net>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>