compose: Rename stream selection widget to "select_recipient".

Previously this dropdown was only for selecting streams, but
soon it will also be for switching to a private message. This
name helps it be clearer that the dropdown is more general
purpose.

web/src/click_handlers.js

@@ -695,7 +695,7 @@ export function initialize() {
         }
 
         // The dropdown menu needs to process clicks to open and close.
-        if ($target.parents("#compose_stream_selection_dropdown").length > 0) {
+        if ($target.parents("#compose_recipient_selection_dropdown").length > 0) {
             return;
         }