bug-34-preload-database-function

@john-hu I have finished bug-34, Please help me review this one. Thank you~
試了一下程式碼，似乎還是覺得這個並不需要，我們應該直接用 DownloadManager 來做到這個, example：
http://developer.android.com/reference/android/app/DownloadManager.html