Switch default installation image link?

[ Note Reply-To: set to d-devel ]

Hey,

For a number of years, we've been linking to the amd64/i386 netinst
installer image from the front page. I think it's time to just switch
that to just an amd64 image for stretch now. The vast majority of the
machines out there are now amd64, and we're asking people to download
useless stuff in such cases. i386 users can still find an image for
download.

I'm *also* tempted to switch from the netinst to the first DVD image
instead - network connections have improved a lot.

Thoughts?

[ Yes, I know that #819664 should fix this but I've not finished
  working there yet, and at this point it's not going to be ready and
  translated in 10 days... ]