Bug 7400: Add auto-completion on auth_finder

Bug 7400: Add auto-completion on auth_finder

While typing an authority, will automatically propose authorities (similar to
autocompletion for patron search if activated)

Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
Tested searching for authorities with and without autocomplete. Note that
this is most useful when used in the "Main entry" box instead of the
"Main entry ($a only)" box.
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
Corrected tabs to spaces in auth-finder-search.inc while resolving merge
conflict.

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>