Feature: Permanently save snippets

[Zlatkovsky]

There have been numerous requests to offer more permanent storage for snippets (be it a GitHub repo, a OneDrive folder, etc.)

We need to think through it.

In the meantime, closing the following two issues from the old repo, to track it in this new one:

• https://github.com/OfficeDev/script-lab-2017/issues/864
• https://github.com/OfficeDev/script-lab-2017/issues/394