Fix: Link.class does not get autopopulated

Due to jquery.slug.js uses the `class` attribute to identify
input tag to populate.
Fix: Don't assume builtin plugins are always active
Configure AttachmentsController for Wysiwyg

This was previously configured in Ckeditor plugin which is the wrong
place to do it.
Removing hardcoded references to FileManager
Fix: getimagesize still triggers a warning for missing files
Fix: check for typeahead_autocomplete before calling
Merge branch 'master' into 1.6