Added contextual translation support (CTranslate and CUTranslate)

The corresponding strings are in the form of "context|text"
The context and the pipe separator must stay as is in the translation.

I did like that because there is no official support of pgettext()
under windows and I prefered a common way to do it.
Added support for c-format string type translations.

And used in game to clarify the concerned sentences.