Config-initialized engine modules

[febret]

In config files, add possibility of initializing engine modules as such:
config file

config:
{
    modules:
    {
        stereoSwitcher:
        {
            class = "CameraStereoSwitcher";
            blah = true;
        }
    };
}

This will call python _stereoSwitcher = CameraStereoSwitcher.create("stereoSwitcher")

create call can use the passed string as the module name, and to lookup config
settings for the module. The _ in front of the module object variable is to assure it does not get destroyed on runtime cleanups (see https://github.com/uic-evl/omegalib/blob/master/src/omega/PythonInterpreter.cpp#L450)

Initialization reads both application and system config files.

This feature can be used to add functionality to app through config files, such as Camera control modules etc. This system is better than adding module initialization to default_init since that script is only executed for applications launched through orun