Move 3rd party storage samples into one repo

[petrbroz]

There are two repos for integrating Autodesk Forge with 3rd party storage providers (Google Drive, Box) that replicate significant amount of functionality. I'd suggest that we move them into one repo, with all providers either combined together, or implemented in individual branches. That way we can easily update/fix the code shared by all providers, and easily add new providers as well.