bug-34-preload-database-function

@john-hu I have finished bug-34, Please help me review this one. Thank you~
I would like to use `custom` made list layout here. 如果只用字串的 layout，它只有單純的一串字，我們還需要在同一個介面上顯示它是否已經下載過，還是下載一半而己。