Check if en-US plugin with the same name exists

* Moved variables to main(), left only outputlevel as global
* Check if a searchplugin file has the same name of an existing en-US
searchplugin. In that case ignore the existing file for json. For en-US
consider all xml files, not just those in list.txt
* wrap XML parsin in try/except to have a more specific error message
* don't print errors on missing descriptions, we're not using them
anywhere