Update strings.xml

Fixed formatting + some bugs from last Pull Request.

The first info was:
 "Bug fixes, improved intelligibility of some strings, the translation is more friendly now (better inflection and in czech "Tykání"). All strings should be translated now. The program was already tested with this new translation.

If any problem or question, please contact me. It is the first time I am using this kind of develop/translate service :-)"