06-a,b: Add download erb page, pass in path for converted gif.

* This route is starting to look really ugly and needs refactoring. * Note that gsub-ing out the 'public/' part of the gif's path is necessary because Sinatra looks for images in the public folder by defaul, making it redundant and breaking the link if it is left in.
Merge branch '06-user-sees-gif' into development

Merge in gif display feature.