Track changes in metadata and update lookup types

[rafaqz]

We should propagate metadata about the operations that have been done on a Raster/RasterStack, what function created it etc.

• aggregate should make lookups Sampled Intervals. They should probably error for categories unless a new lookup is provided.
• mean, max etc over a dimension should be track in metadata in a way that can be written to netcdf.
• resample, warp etc should be tracked in metadata with arguments included