Update Czech translation

I've created a new MR, because I messed up the commit history.

Here is the updated Czech translation for the latest version.

In the previous update I've corrected some of the mistakes and updated the translations to match the Czech GNOME conventions. Now I updated the missing strings.

I really like this app and I believe a lot of people in Czechia do as well. So I think the Czech translation for this app is really important.