Language Convert class: Let users choose site idiom

This class can be used to let users choose the current site preferred idiom.

It can present links to let the users choose their preferred idiom from a list of available idioms.

The selected idiom is determined in assigned to a session variable so the rest of the site can check it to determine which idiom will be used.

The class desing a language handling, with optional links to choose the other languages (to be used in a form, for instance).