Add native spellcheck to CKEditor

As the native spell checker is disabled by default, this PR removes the default behaviour and restore it to check for spelling and grammar in wysiwyg editor.

See : https://ckeditor.com/docs/ckeditor4/latest/features/spellcheck.html#native-browser-spell-checker

htdocs/core/class/doleditor.class.php

@@ -225,7 +225,8 @@ class DolEditor
                                                             breakAfterClose : true
                                                         });
                                                 }
-                                            }';
+                                            },
+									disableNativeSpellChecker: false';
 
             	if ($this->uselocalbrowser)
             	{