Previously it only provided the list of all public streams; now it
allows one to specify any union of some of the following:
* all public streams
* all streams the user subscribed to
(the most relevant being the union of those two, which is what we want
for the "streams" page).
Or:
* all streams in realm (superuser only)
The manual task required is that when this is pushed to prod, we need
to also deploy the new sync-public-streams version to zmirror.
(imported from commit 27848b8bd136e2777f399b7d05b2fdcec35e4e21)
When we deploy this, we'll need to of course actually build and deploy
the new API tarball.
(imported from commit 03c853e8a9424a63f1c74bb83637d5a1e50a159a)
