chore(ckeditor): upgraded CKEditor to version 4.3.2

Fixes #6500
chore(ckeditor): adapted plugin to work with CKEditor 4

Theme changed to moono, so removed specific BootstrapCK-Skin CSS
CKEDITOR.basePath wasn't working for plugins, so defined CKEDITOR_BASEPATH
Fix applied in #5689 is no more required
Wordcount own code replaced by wordcount plugin
Set allowedContent to true to do not filter tags (htmlawed already does it)
Configured new AutoGrow plugin