Top-level Werkzeug imports are deprecated, removed in 1.0

[davidism]

Werkzeug is deprecating then removing most of the top-level attributes in favor of direct imports.

Instead of from werkzeug import ImmutableDict, it becomes from werkzeug.datastructures import ImmutableDict.

The docs have mentioned this for years, but the code only recently started showing deprecation warnings. It would be great to get this out as a point release, as Werkzeug 1.0 will be released within a month and will remove these deprecated imports.