Bug 30204: Add subtitle to serial search results

Bug 30204: Add subtitle to serial search results

To test:
1. Make some new serial subscriptions and connect them to biblios that contain subtitles.
2. Do a serial search that will return your newly created subscription.
3. Notice the subtitle doesn't appear.
4. Apply patch and restart_all
5. Again try step 2.
6. Notice the subtitle appears alongside the title now.
7. Make sure it still sorts that column correctly.

Signed-off-by: shiyao <shiyao@inlibro.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>