This commit migrates all webhooks to use check_send_stream_message
instead of check_send_message. The only two webhooks that still
use check_send_message are our yo and teamcity webhooks. They
both use check_send_message for private messages.
All webhook fixtures in zerver/fixtures/<webhook_name> have now
been moved to dedicated webhook-specific directories under
zerver/webhooks/<webhook_name>/fixtures, where <webhook_name> is
the name of the webhook.
I dug into why we never did this before, and it turns out we did, but
using `$.trim()` (which removes leading whitespace as well!). When
removing the `$.trim()` usage.
Fixes#3294.
Eeshan Garg
rht
Tim Abbott
Tomasz Kolek