[tut/chap2] adjusted prose describing scope and model etc

- adjusted prose describing scope and model
- Prefix annotation class name occurrences with @ for better
readability (and it more std).
- cleaned up some whitespace in code snippets
Merge pull request #15 from chalin/patch-15-adj-scope-and-model-defn-ch2

[tut/chap2] adjusted prose describing scope and model etc
Fixing mirrors used.
Merge pull request #18 from blois/mirrors_2

Fixing mirrors used. Thanks, @blois!
Merge branch 'master' of github.com:naomiblack/angulardart.org

Conflicts:
	app/dart/examples.dart