Image url

Created a field in the database, associated forms and views, spec tests, and validator in lib/validators that allow a user to include an image with their project description by linking to a file hosted on a whitelisted website.

https://www.pivotaltracker.com/story/show/80235250
non-blocking issue, the indentation on this line is a little too large, if you happen to pass by this file, could you fix the indentation and keep it consistent?