Bug 28904: Fix typo and display

Bug 28904: Fix typo and display

Fix typo in template: Newletter => Newsletter
Fix latest newsletter editor definition.. it's a has not an array.

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 ded631f39e82352a713a252af714b4e2907c4c2f)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
(cherry picked from commit f0695c74201fa4d2a8ddd22b7eddf91d1a72d6d8)
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>