Add images to user and projects

Allow users to upload a photo of themselves and a project photo.
This commit includes: configure carrierwave, fog and aws, add
image columns to user and project tables, add image upload field to the user
and project forms, display image thumbnails in index pages, and display
 larger images on show pages. Rationalize some of the related CSS.
The default image is going to change in a future update, which will result in a shorter line, so I'll leave this for now.