popup.html: the website setting does not work

[kite1988]

A few issues about the website setting:

• The check/uncheck does not have any effect on the extension. That is to say, the extension still translates words in an unchecked website.
• The javascript/html uses hard-coded indices for the three websites, which is not a good idea.
• The 'chinadaily" website is not supported, and thus just remove it from the popup.html and the relevant javascript code.