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
One other issue is the file name, the name looks better but there is still the “v1” at the end. There is no need to add a version for the migration, the timestamp does a pretty good job of versioning the file.