Support redirect style Logins

Signature:

```js
Hull.login({
  provider:'facebook',
  strategy:'redirect' //'redirect'||'popup',
  redirect_url:'http://example.com' //optional, only used for strategy=redirect
});
Hull.login({
  login:'user@example.com',
  password:'12345',
  strategy:'redirect' //'redirect'||'popup',
  redirect_url:'http://example.com' //optional, only valid for strategy=redirect
});
```