WIP implemented carrierwave functionality

Users now have the ability to upload a single picture to use as their profile picture. They can choose between jpgs, gifs, etc. Still need to work on multiple images, and need to make sure that it doesn't break if a user chooses not to upload an image. In place of an image, that user's profile should contain a default Stack Overflow picture (much like Gravatar). Also, clicking on a user picture should link to the full size version.