Code maintenance: accessing global settings properties from session objects

[confluence]

We currently pass config settings values into session objects in two completely different ways:

1. Using static functions to set static properties on the Session class:

if (settings.wait_time >= 0) {
    Session::SetExitTimeout(settings.wait_time);
}

if (settings.init_wait_time >= 0) {
    Session::SetInitExitTimeout(settings.init_wait_time);
}

2. Passing them into the Session constructor:

_sessions[session_id] = new Session(ws, loop, session_id, address, _settings.top_level_folder, _settings.starting_folder,
        _file_list_handler, _settings.read_only_mode, _settings.enable_scripting);

2 doesn't really make sense. These properties don't change per session; they're global properties which remain unchanged for the lifetime of the backend. They should all be static.

Rather than duplicating most or all settings values as static properties on Session, however, I think it would be cleaner for us to turn ProgramSettings itself into a singleton which is initialised in Main and can be imported from any part of the code and used to access the settings properties directly.

[confluence]

Clarification: there should be a single ProgramSettings object which is initialised and made accessible through some kind of static function. Code which needs to access the settings should then refer to the settings object properties directly. That will remove the need to copy these values and pass them around explicitly.