Bug 31028: Add configurable help text and templates

Bug 31028: Add configurable help text and templates

This patch adds configurable help text and a template option to the
catalog concern report modal in the OPAC.

Test plan
1) Enable `OpacCatalogConcerns` preference
2) Build the CSS for the OPAC
3) Check that there is a 'CatalogConcernHelp' block listed in the HTML
   Customisations page.
4) On the OPAC navigate to a record and click the 'Report a concern'
   button.
5) Confirm that the content of 'CatalogConcernHelp' displays beneath the
   detail entry box and that it displays as expected.
6) Check that there is a 'CatalogConcernTemplate' block listed in the
   HTML customisations page.
7) On the OPAC 'Report a concern' modal, you should see the content of
   the 'CatalogConcernTemplate' block pre-filled in the details
textarea.

Note: There is a caveat to the template.. as textarea can only be used
to submit plaintext with this patch and as such the template needs to
not utilise the WYSIWYG editor else you will be faced with raw HTML
inside your textarea.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Helen Oliver <HOliver@tavi-port.ac.uk>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>