Bug 25954: Replace paragraph tags with labels in header search forms

Bug 25954: Replace paragraph tags with labels in header search forms

This patch replaces instances of <p class="tip"> with <label
class="tip"> in header search forms where there is not already a label
tag corresponding to the first form field.

In cases where there is already a label on the first form field the <p>
is kept.

To test, apply the patch and rebuild the staff client CSS
(https://wiki.koha-community.org/wiki/Working_with_SCSS_in_the_OPAC_and_staff_client)

Test the header search forms on the following pages:

 - Staff interface home page
 - Acquisitions home
 - Acquisitions -> Vendor -> Contracts
 - Acquisitions -> Vendor -> Add to basket -> From a suggestion
 - Advanced catalog search
 - Authorities
 - Administration
 - Administration -> Funds
 - Administration -> Desks (UseCirculationDesks must be enabled)
 - Administration -> Cities and towns
 - Administration -> Currencies and exchange rates
 - Administration -> Patron categories
 - Administration -> Z39.50/SRU servers
 - Catalog -> Search results
 - Cataloging
 - Circulation
 - Circulation -> Check in
 - Patrons
 - Serials
 - Tools -> Notices and Slips

In each case, check that the search form labels work as expected to move
focus to the corresponding form field.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>