Extend export plugins to support web access

I'm thinking this could be part of the base class, so that that all export plugins benefit, but if that is difficult then just the XML plugin needs it:

The basic idea is to build a way to pump gradebook data out via http like a very simple web service.

So imagine some settings addded to the initial screen to:

Publish these grades via URL: [X]

Limit client IPs to: |__192.168.2.2, 135.6.78.99 _______________| (highly recommended)

Require password: |_snoopy123__|

If this checkbox is on, then the data is not sent to the screen and downloaded as a file like usual, instead you see a page which gives you the URL to access this data in a simple way, eg something like:

http://test.moodle.com/grade/export/xml/dump.php?courseid=3&items=4,5,6,7,8,10&password=snoopy123

which can be cut and pasted elsewhere.