Streamline set up of dependencies.

Separate out external dependencies into a new directory (ext_lib).  Provide a helper bash script to download these.  Restructure include path such that these can be included verbatim.

Updated .gitignore to ignore these external dependencies in addition to other sensitive files such as client_secrets.json.
Convert fractal demo to use user's project.

Follow the pattern of the other demos and stop using robot accounts with a hard coded project for the fractal demo. Along the way, fix up the need to have a custom image (it is optional and detected).  There is still a hard coded shared bucket for the assets needed in the VM.

Also remove unnecessary scope from the service account set up for the VM itself.  None of our demos require the VM to call the GCE API.
Change source of dependencies to grab from code.google.com.

Also added instructions on how to add new dependencies.
Merge pull request #3 from jbeda/master

Some simple clean ups