Feature: Snippets

[migueldeicaza]

We should have a way of having snippets that people can use, and ship a few by default.

Snippets could also list hosts where they automatically execute.

• [x] UI for defining snippets
  • [ ] Include a way of flagging them to be limited to an OS
• [x] Loading/saving snippets
• [x] Surface snippets on the toolbar
• [ ] Snippets top-level to run on hosts