i18n: Add missing Czech translations

[ceskyDJ]

I'm sorry to be late with Czech translations. Next time, when some string changes, you can tag me in a commit message, pull request, etc.

[lneugebauer]

Hey @ceskyDJ, no worries.
Since I probably won't remember to tag you every time I make changes to the strings. Have you tried using the Github File Watcher? You could set it to watch the default strings.xml file (app/src/main/res/values/strings.xml) and get notified every time it changes.
This would ensure that you are notified every time! :)

[ceskyDJ]

Ok :). File watcher looks as a very good idea! Thanks for mentioning. I didn't know Github has something like that at all :(. Ok, it is 3rd party thing, it makes sense :D.