Migrate apptask to use tasks framework

src/taskworker.js

@@ -2,7 +2,8 @@
 
 require('supererror')({ splatchError: true });
 
-var assert = require('assert'),
+var apptask = require('./apptask.js'),
+    assert = require('assert'),
     async = require('async'),
     backups = require('./backups.js'),
     database = require('./database.js'),
@@ -16,6 +17,7 @@ var assert = require('assert'),
 const NOOP_CALLBACK = function (error) { if (error) debug(error); };
 
 const TASKS = { // indexed by task type
+    app: apptask.run,
     backup: backups.backupBoxAndApps,
     update: updater.update,
     renewcerts: reverseProxy.renewCerts,