[WIP] Initial support for a plot area with multiple different charts on it

- Added basic BarChart (the non-3D version)
- Added initial multi-chart support.  It's a bit of a hack right now.

This is going to need a lot more work to properly support, but I'd like to get your thoughts on the feasibility of moving forward with something along these lines.  I have need of such support for a project, so will be working on this stuff for awhile.

Unfortunately, I think that over the long-term the concept of a "chart" and "plot" will need to be separated - right now they're somewhat grouped together but I feel that's going to cause more issues than not in the long term.