Some translations in the "admin" folder

[msi]

Michael missed something from my ticket #608. There was a second line in "plugins.php". I do not blame him, I just saw it right now.

I also changed the sentence for the license in "themes.php". And I removed that little "v" (for the version number). I do not think it is necessary. Do you?

The third change is in "groups.php". I think this file is under construction. I changed two sentences, though, because including the placeholder %s within the term can make the translation more fluid.