Bug 22343: Allow choosing an SMTP server in branches.pl

Bug 22343: Allow choosing an SMTP server in branches.pl

The missing piece on this patchset is choosing the desired SMTP server
for each library. This patch adds the option on editing the library.

The default one is picked for existing libraries, and you can pick the
one you want.

To test:
1. Apply the patchset
2. Run:
   $ updatedatabase
=> SUCCESS: Things go smooth
3. Notice the new permission for managing SMTP servers
4. Notice the entry in the admin page
5. Add/have a few SMTP servers defined.
6. Edit a library
=> SUCCESS: The 'Default' SMTP server is picked
7. Choose any server and save
=> SUCCESS: Saving doesn't explode
8. Edit the server
=> SUCCESS: Your selection is kept (this can also be checked on the DB,
        the library_smtp_server table)
9. Try (7) with many different options
=> SUCCESS: It works
10. Sign off :-D

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>