[cobalt.conf] better default configuration

[ggendre]

main idea

remove default controller and move ALL default values to the root of the JSON.

More on this

All values that can be defined for a controller can be defined at the root level of the JSON, including bars, iosController, background and so on.

As the list of thi settings may be larger inb the future, we will need to rework the cobalt.conf parsing so that it will be easy to handle future default values for future settings.

This default value stytem is recursive : The controller values and the default values should be combined recusivelly. For example, with the following cobalt.conf, the title color of myPage will be white.

{
    bars :{
        color:'#fff',
        backgroundColor : '#000'
    }
    controllers : {
        myPage : {
            bars : {
                title : "Hello"
            }
        }
    }
}