Filter behaves similarly to filter in left sidebar, see PR #684. Added
stream input field to the stream creation modal along with other settings,
for clarity.
Fixes#455, #563.
If a user is not allowed to create new streams, then do not
show the "Create new stream" UI at the top of the settings page.
(imported from commit b97626938d8b612317c2189f7eca0d4bd27fc274)