authenticate administration page

[kjdon]

Some people would like to have the entire administration pages needing authentication, rather than just the add user bits.

This is easy to do in the code: in check_cgiargs in statusaction.cpp, always set

    args["uan"] = "1";
    args["ug"] = "administrator";

We need to make an option in main.cfg for this so users don't need to edit code to achieve this.