Add info about AppView.
Reduce overly redundant AppView reference
Corrected a to an
Added code-block annotations
Use custom helper instead of HtmlHelper in example.
Fix formatting.
Merge pull request #1877 from cakephp/3.0-app-view

Add info about AppView.
[fr] updates

follows
- #1868
-  09df18b7
-  2a7b79d8
- 0fac7d25
- #1875
- 12f68611
follow #1877