Use the Client class in client.c file

This simplifies a lot the client code.
Convert printf -> std::cout and fix some endl
Rename CFLAGS -> CXXFLAGS
Better way to make server verbose

Now use just an Make variable to enable it or not and use string concatenation in C++
to build the strings that will be verbosed.
Convert send_messages_to_user to use std::string

This help us to avoid the creation of a temp var
We already have a minimal ncurses prototype :-)