Bug 7411: Remove diacritics from generated userid

Bug 7411: Remove diacritics from generated userid

Patch introduces a new module Text::Unaccent.

To test:
1) Add a new patron with diacritics in surname and first name, leave userid empty.
2) Save user and check the created userid has only the base characters and
diacritics have been removed correctly.
3) Create another user with the same surname and first name, check userid
is generated correctly.

Signed-off-by: Dobrica Pavlinusic <dpavlin@rot13.org>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>