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.
This one is weird: without the ".any?" the else clause doesn't get called - it's like current_user.projects isn't being treated as "truthy". It took me a while to figure it out.