Bugzilla/936703/call screen indexeddb abort error

There is a small chance that WindowManager terminates CostControl app when it's still processing IndexedDB calls. This pull request add an optional `asyncStorage.oncomplete` callback slot so that we have a chance to delay `Common.closeApplication()` call in it.  See [bug 936703](https://bugzilla.mozilla.org/show_bug.cgi?id=936703).