Rearrange eutopia to use __all__ exports.
repair 'import simulation' which died with ReferenceErrors

I'm not sure what I did that broke it. The changes I made shouldn't
have been structural like that. Where did num_steps come from previously??
Export the relevant variables at the top level (and *only* the relevant variables).

That is, 'from eutopia import *' now hides private and privateish members,
 like pygdal (which shouldn't be here in the first place) and
but this is python afterall, with batteries included and trust in the programmer,
so 'import eutopia' or 'import eutopia.pygdal' will give full access as usual

This only took like thirty friggin hours to figure out.
patch server.py to use the package changes I made to eutopia. Cleaner!

Also, stub out running create_demo_model() inside server.py; this
 will let me tackle the "Module runs slowly" bug, which doesn't
 show up under the command line version of Eutopia (so, it makes me
 think there's something weird with how .intervene() is being called
 inside server.py)