Move language reading direction definition ("dir") from main language file to core

[Wiktor Walc]

It happens quite often that translators confuse the "dir" entry in main language file and try to translate it into something (e.g. between 4.1 and 4.1.1 release two language would get broken because of that).

Since we already store information about available language files in core/lang.js (CKEDITOR.lang), I'd like to propose moving this meta information about a language also to core.

Language files should contain only things that are supposed to be translated. Any other information should be moved outside of it.