UploadToCPAN: load File::HomeDir when used

... and don't import its 'home' function.
GatherDir: load File::HomeDir when used

... and don't import its 'home' function which is in @EXPORT.
Command 'add': load Path::Class and File::pushd only on 'execute'

... because every Command plugin is loaded even if not called, so
plugins must use lazy loading.