Add info for App.paths config.
Removed misplaced note.
Add info about App.paths.locales to migration guide.
Add info about Router::defaultRouteClass()
[fr] follow #2026
Try and address some pitfalls in the bookmarks tutorial.

Refs cakephp/cakephp#5200
Move defult route class section below section for custom route class.
Merge pull request #2028 from cakephp/bookmark-auth

Try and address some pitfalls in the bookmarks tutorial.
[fr] follow 806a80806a28228409fe228f8a7528ef786ba9a4d97446 & fix fr translation
[fr] follow #2022, 6d4f70d, e30d736 and #2028
Merge pull request #2026 from cakephp/3.0-misc

3.0 misc