Add a 'gama' agent available in experiments/simulations

[AlexisDrogoul]

… with machine_time, paths, memory used, version of GAMA, version of Java...

[AlexisDrogoul]

This agent could become the host of experiment agents, provide a default scope (so that a scope is always available), serve as a support for system-related variables (machine_time, etc.), but also preferences (allowing to change them on the fly), properties (gui or not gui, for instance), and provide actions to create/run/stop experiments, load files, etc.

It would be the default agent with whom the interactive console is connected (allowing this console to be active in modeling perspective as well).

[AlexisDrogoul]

Work has begun on this one, with already a platform built-in species that allows to create agents and give them the possibility to change system preferences in models.

something like:

global {
    init {
        create a;
    }

species a parent: platform {
    init {
        pref_experiment_auto_run <- true;
    }
}

is already possible.