feat(core): Update to ckeditor 5. Fixes #5920. Add SOGoForceRawHtmlSignature to disable raw-html-embed. Removed CKEditor signature box style when composing mail. Fix issue where raw-html-embed was added when changind signature

SoObjects/SOGo/SOGoDomainDefaults.m

@@ -465,4 +465,9 @@
   return emailFrom;
 }
 
+- (BOOL) forceRawHtmlSignature
+{
+  return [self objectForKey: @"SOGoForceRawHtmlSignature"] ? [self boolForKey: @"SOGoForceRawHtmlSignature"] : YES;
+}
+
 @end