New redirect strategy

I change the way the redirect strategy works.
The redirects from authenticate/logout actions are now callbacks.
This way the user can overwrite the default callback and decide **exactly** what to should happen.

ping @Ocramius

closes #479
closes #476
closes #473
closes #469
Another thing: where do you the the route parameter from? I don't see a route definition in this PR which adds a parameter to the route called `redirect`, so I assume now this is always false?