Sorted donors, dont show logos of lowest tiers

OK, so I worked on this last night at the meetup, so lets see what is left to be done. Here is a image of it as of this PR (sorry about images, they were picked randomly off my desktop....)

![](http://i.imgur.com/l8Eb9FK.png)

You see how the images in the upper tiers do have images, but the lower tiers do not (even though there is a image associated with the donor)

This changes the way donors are ordered, with the highest tier ("AWS") first, and going down to the lowest ("Other"). This also discludes showing of images for the "Other" and "Individual" tiers. I find this good in practice because all upper tiers have logos, so it is good to show those tiers, while the lower tiers may not have images, so its better not to show them.

Feedback welcome!