Accounting for all land cover types

[ksmiff33]

Thinking about how we develop projections for our natural systems, and one thing that's missing is a data frame that includes ALL land cover types (not just the natural systems ones). Say for instance we want to model a scenario where 10% of impervious land is converted to a forest – we already have an estimate of forest cover, but not impervious cover (per se). So the goal with this issue is to export a data frame for counties and CTUs that includes area for all land cover types for each year.