Implement Snippet Completion

Scratch could benefit from a snippet completion plugin/feature.
This would greatly increase it's usability for programming, it is a real time saver.

Here is a video showcasing what snippet completion looks like, http://www.youtube.com/watch?v=U3wCBm9_hik

Essentials:
Creating snippets
Invoking them with a shortcode and a tab
Tabbing between parameters on a created snippet

Extras:
Saving snippets into a server like github
Fetching snippets available on public repositories
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