[tutorial] Chap 5: introduce ng-switch and new exercise

- Use opportunity to introduce ng-switch for the conditional display of
"Loading ..." message.
- Summary: mention that Chap 5 covers JSON, ng-switch.
- Chap. 5: add extra exercise (building upon the first two).
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Merge pull request #36 from chalin/patch-0226-chap5-varia

[tutorial] Chap 5: introduce ng-switch and new exercise
Update 07-ch05-filter-service.html
Update 07-ch05-filter-service.html
sync with the code

replaces #19
Merge pull request #38 from vicb/patch-5

sync with the code
Add details about how Angular manages `ng-app`

replaces #18
Merge pull request #39 from vicb/patch-5

Add details about how Angular manages `ng-app`