finish capturing a session
function () {
			var self = this;
			console.log('stopping capture...');
			var req = get_req();
			req.onreadystatechange = function stop_capture_response () {
				if (req.readyState === 4) {
					self.update_state();
					console.log('stopped.');
					jQuery("#stop").hide();
					jQuery("#start").show();
          htracr.ui.unpulse_logo(true);
				}
			};
			req.open("POST", "/stop", true);
			req.send("");
			return false;
		}