Initial Czech localization

There are some keys which cannot be translated always well, because Czech pluralization rules are more complex than English ones (1)(0,2...). We may have different words for (1)(2,3,4)(0,5...) counts. Some other languages may be even more complex I think [1].

A list of affected keys:

"days left"
"You have %ld desktops"
"You need %ld desktops"
"desktops, and"
"full screen apps"

[1]: http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/language_plural_rules.html