When the user creates a stream, we no longer do a synchronous
check on the back end to find if the stream name already exists.
Instead, we only check our local data, which will prevent many
typical errors, and then we let the back end capture duplicates for
stream names that the client doesn't know about.
We also tone down errors when the stream name is blank--we
only whine about empty streams right before submitting the form.
Also, since our check for duplicate streams is less expensive,
we now capture the "input" event instead of the "focusout" event,
so that if you fix up the name to avoid a collision, you get more
immediate feedback.
When we do detect stream name errors, we conveniently focus the
text field to let the user correct the problem.
This new modules handles the UI to create streams. It mostly moves
code from subs.js.
It introduces an API around what used to be called meta.stream_created:
reset_created_stream()
set_name()
get_name()
It only partially moves new_stream_clicked().