Improve calculations of multi language widgets

**Is your feature request related to a problem? Please describe.**
Projects often have a large list of languages for translations, but at the same time most of those languages have no translation at all (0%). That causes a ridiculous size of the widgets showing multi language status. See screenshot below, or check https://hosted.weblate.org/widgets/planner/#horizontal


**Describe the solution you'd like**
I think it would help, if all languages with 0% don't show up in the widgets, as it much better represents the _real_ status of projects.

**Additional context**
Omitting languages with 0% would also mean, that all widgets would have to be recalculated for "number of languages" and for "translated percentage". I'm aware it's some additional work from your side, but I think it's just some simple math which needs to be implemented.