Allow type definitions to restrict views; this specifically
supports the restriction of autoflow tabular views to packets,
and the omission of scrolling/plot views as applicable to
packets. WTD-644.
Warn if a view definition does not include a key,
and prune it from the list of views. This avoids
an underlying cause of WTD-628, which is fixed for
plots specifically in the previous commit but could
recur if other views were to omit keys.
