Add ability to search entire message history of all public streams at
once. It includes all subscibed, non subscribed public streams messages
and even historical public stream messages sent before user had joined
an organization or stream.
Fixes#8859.
Add all the stop words to page_params, reading from the
`zulip_english.stop` database, with caching to avoid loading the file
on every page load.
Part of #10592.
Also, fixed up the annotations for tornadoviews to better align with
how narrows was defined as `Iterable[Sequence[str]]` rather than
`List[Tuple[str, str]]`.
This will allow us to substantially decrease the server-side work that
we do to support our Mirroring systems (since the personal mirrors can
request only messages that user sent) and also is what we need to
support a single-stream Zulip widget that we embed in webpages.
(imported from commit 055f2e9a523920719815181f8fdb44d3384e4a34)