-Add a Backend::package() overload that takes a QLatin1String. If you can use this overload, it is more efficient since you don't have to go QString -> ascii -> latin1 -> const char
-Make the regular Backend::package() implementation use the QL1S overload. This is slightly more efficient since we can convert directly from QString -> latin1 without converting to ascii in between (since APT package names will always be standard ASCII)