Updated Proxy_Editing_Toggle for fullres

Proxy_Editing_Toggle now takes into consideration original fullres files that have no _PRORES or _MJPEG in their name. 

This will often be the case for users that will choose to create proxies using the addon but will use her/his original files (e.g. an .avi from a camera or a .flv from internet) for the final render, instead of a prores422/mjpeg copy that would have been created by the plugin.