[tutorial] Chapter 5 mismatches with code fixed

- Code excerpts did not reflect fixes applied to tutorial code:
    1. HTML input still had value attribute (#44).
    2. `main.dart`, first excerpt of `MyAppModule()` showed old style
injection.
    3. `_loadData()`: used `onError:` instead of `catchError()`.

- Also removed unnecessary whitespace in some code excerpts.
- Prose still needs to be reworked but I need to call it a day.
Merge pull request #9 from chalin/patch-10-chap-05-fix-mismatch-with-code

[tutorial] Chapter 5 mismatches with code fixed