plugininstall.cgi: Show "Downloading" if plugin url
plugininstall.cgi: Show "Downloading" if plugin url

Closes #958

mschlenstedt/Loxberry,mschlenstedt/Loxberry,mschlenstedt/Loxberry,mschlenstedt/Loxberry,mschlenstedt/Loxberry,mschlenstedt/Loxberry