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
Move defult route class section below section for custom route class.
[fr] follow 806a80806a28228409fe228f8a7528ef786ba9a4d97446 & fix fr translation
Merge pull request #2026 from cakephp/3.0-misc

3.0 misc