Split cell copier logic out of Grid

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Please describe use-case:

Introspection in Java is slow.

The way we copied cells in the Grid class required both introspection and a 
little try-and-fallback.

There are faster ways if we know what type we're copying.

We should have a way of specifying specific cell copiers so that we can speed 
things up.

This is done, but I didn't have a ticket for it.

Original issue reported on code.google.com by yam...@gmail.com on 7 Aug 2012 at 3:03