Bug 28525: Dont let TinyMCE do code cleanup

Bug 28525: Dont let TinyMCE do code cleanup

If you look at Bug 24764 and Bug 26942 we adjusted the TinyMCE for the News tool so it will not do some types of automatic code clean up.

The TinyMCE editor for system preferences which can be enabled by 'UseWYSIWYGinSystemPreferences' has the same problems.

We should make the configurations the same.

To Test:
1. Turn on 'UseWYSIWYGinSystemPreferences'
2. Go to a system preference like 'RestrictedPageContent'
3. Try entering something like '<i class="fa fa-facebook-official" aria-hidden="true">TEST</i>' in the Source Code window
4. It gets cleaned up by the editor
5. Try something like '<a href="https://www.test.com" referrerpolicy="&quot;no-referrer-when-downgrade">TEST</a>'
6. It's cleaned up by the editor.
7. Try something like '<link href="https://fonts.googleapis.com/css?family=Open+Sans” rel=“stylesheet">'
8. Cleaned up by editor.
9. Apply patch
10. Try step 3, 5, and 7 again.
11. It should not be changed by the editor

Signed-off-by: Barbara Johnson <barbara.johnson@bedfordtx.gov>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 995d080e39230305dc6d3336db8ca2ab6308e829)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>