Bug 19987: If no z39.50/SRU servers the button should not show

Bug 19987: If no z39.50/SRU servers the button should not show

Test plan:
[1.] Load the patch and make sure you have some Z39.50/SRU servers
     (Administration => Z39.50/SRU servers administration)
[2.] Then go to authorities and notice that the 'New from
     Z39.50/SRU' button is there
[3.] Next go to cataloging and notice that the 'New from Z39.50/SRU'
     button is there too
[4.] Now make sure you have no Z39.50/SRU servers (remove the
     servers)
     (Administration => Z39.50/SRU servers administration)
[5.] Go to authorities and notice that the 'New from Z39.50/SRU'
     button is not there
[6.] Lastly go to cataloging and notice that the 'New from Z39.50/SRU'
     button is not there too

:)

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
I added a missing [% END %] during signoff. Hope no one minds!

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>