Fix gen_mod indentation before introducing changes
Add set_module_opt/4 to alter module config at runtime
Perform minor gen_mod cleanup
Make BOSH inactivity period configurable at runtime
Fix readability
Extract stream_start
Use unique message tag

Message {send, _} is used for send/2 ejabberd_socket API function.
Change the tag to avoid ambuity.
Disconnect BOSH clients on inactivity