Remove any frontend related code in Interface/System

[paraboul]

require("OS").language doesn't seem to work on linux (returns undefined).

[verpeteren]

Indeed 'os.language' is not present in nidium-server, only in nidium (frontend). It is wrapped inside a ifdef block to protect calls to Nidium::Interface::SystemInterface::_interface.

It might be that this is an relict of the historical repository split. Please advice what road to take:

• nidium-server should have access to _interface in the same way as nidium (frontend).
• leave it as it is now, close this issue

[paraboul]

Indeed.

There is a confusion between Interface and System. We should reorganize the code in System to remove any frontend related code.