Pass non-named routes through Form::open()

You can now pass non-named routes alongside urls to Form::open with the 'url' parameter. The UrlGenerator will validate if it's a valid url and will otherwise try to generate an url if it's a route.

Signed-off-by: Dries Vints <dries.vints@gmail.com>
Merge pull request #515 from driesvints/dv/non-named-routes-for-form-open

Pass non-named routes through Form::open()