Make Mojolicious::Validator supports named routes

At the moment, Mojolicious::Validator only preload parameters from GET's url or POST's body. It will not load the parameters from a named route by default. $validation->input has to be called explicitly for named route parameters.

This commit lets Mojolicious::Validator preload the parameters from named routes as well.

I have amended the corresponding documentation and added one test case in validation_lite_app.t.
This line is formatted wrong, the description "named routes" is inconsistent with all our other documentation and precedence is not mentioned. http://mojolicio.us/perldoc/Mojolicious/Controller#param