Fix werkzeug.wrappers.BaseResponse.__init__ (#2232)
Fix werkzeug.wrappers.BaseResponse.__init__ (#2232)

This additionally allows strings, bytearrays and string iterables to be
passed as the `response` argument of `BaseResponse` (and thus also
`Response`).

Strings and bytearrays are explicitly handled in `__init__` [1].
Strings are also featured on the Werkzeug front-page snippet (`'Hello
World!'`) [2].

[1]: https://github.com/pallets/werkzeug/blob/d129d17066768238139b8f8a5d667d9a4f4d68db/werkzeug/wrappers.py#L861
[2]: http://werkzeug.pocoo.org/
euresti/typeshed