Add support for only publishing a language if it more than NN% translated #16
Description
When the source material keeps changing, the translations will naturally lag behind. In that case, it could be nice to only publish a new version if it mostly up-to-date, meaning it is more than NN% translated.
This kind of functionality can be built today by looking at the output of msgfmt since it shows the number of translated and untranslated messages. We should try to package the functionality in a reusable fashion.