Bug 31605: Improve style of OPAC suggestions search form

Bug 31605: Improve style of OPAC suggestions search form

This patch makes minor modifications to the markup for the
OPAC suggestions search form so that the different labels and
form fields display a little more nicely.

The patch also adds standard Bootstrap alert classes to
several messages which might be displayed on the screen, e.g.
"You have no pending purchase suggestions."

To test, apply the patch and make sure the "suggestion" system
preference is enabled.

- With the  OPACViewOthersSuggestions preference disabled, log
  in to the OPAC and view your suggestions.
- If you have no suggestions you should see a Bootstrap-styled
  message box, "You have no pending purchase suggestions."
- If necessary, submit a suggestion. With at least one suggestion
  present you should see a search form above the table of
  suggestions. The label, form field, and submit button should
  line up nicely.
- Test that the search form works correctly to find suggestions
  in your system.
- If you search for a suggestion which doesn't exist you should
  see a message-style alert, "There are no pending purchase
  suggestions matching your search."
- Enable the OPACViewOthersSuggestions system preference.
- Return to the OPAC suggestions page. The form field should
  now include a nicely-styled "Suggested by" filter.

Signed-off-by: George Williams <george@nekls.org>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 74a1ea73f398a763c69ea409e71a4acaf8eac0c5)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
(cherry picked from commit 31ac74eb0cb018d18006e2261fc7735319d54a45)
Signed-off-by: Arthur Suzuki <arthur.suzuki@biblibre.com>