[IMP-dev] Remaining open questions

[Daniel Russel <drussel@gmail.com>]

1) Hiding the Index classes and making attributes accessed only through 
the Particles themselves rather than through the ModelData. This 
simplifies things a lot and we should be able to optimize away most of 
the overhead later if needed.
2) Decorator classes

I vote yes for both :-) And (1) should be done sooner rather than later 
and effects the DerivativeAccumulator.