Change HTTPS to HTTP for the images that are passed to /iu/ 

Fixes #232. I went through the Spice instant answers that use the `/iu/` endpoint, and I changed Google+, Video, and Khan Academy. The command that I used to search through the plugins was `fgrep -nr "/iu/?u=" share/`.

The only thing that I wasn't able to change was Quixey. The problem is that we're using https://i.quixey.com/image/2742316565 which redirects us to https://d1z22zla46lb9g.cloudfront.net/image/2742316565. 

Now there is a dirty workaround: We could get the cloudfront.net domain from the platforms array

![screen shot 2013-10-22 at 12 13 14 pm](https://f.cloud.github.com/assets/81969/1382921/faea6ccc-3b34-11e3-95aa-fdf437262e9f.png)

and then append that domain to the `icon_url` link

![screen shot 2013-10-22 at 12 14 55 pm](https://f.cloud.github.com/assets/81969/1382930/2088c2e4-3b35-11e3-8597-fb3843252a12.png)

which gives us http://d1z22zla46lb9g.cloudfront.net/image/2742316565 -- the link that we want. I'm not sure if that's the best way, though. @moollaza maybe we can talk about that sometime.