Major change to dataviews requiring compatibility changes

Dataviews now have Dimension objects eliminating the cumbersome
dimension_labels and dim_info parameters and unifying Dimensions
in dataviews and Features in featuremapper. May cause some backward
compatibility breakage. If you urgently need to load an old snapshot,
request legacy support to be implemented, otherwise legacy code
will be finalized once dataviews and featuremapper are more stable.