Added VaadinHttpService

Vaadin Http Service
Allow access to HttpServletRequest / HttpServletResponse

This can be used for example to set the REMEMBERME Token.

Example Usage:
```java
@Autowired
HttpService httpService;
...
HttpServletRequest request = httpService.getCurrentRequest();
request.setAttribute(AbstractRememberMeServices.DEFAULT_PARAMETER, rememberMe);
```

Original code from: https://github.com/markoradinovic/Vaadin4Spring-MVP-Sample-SpringSecurity
Original Author 'Marko Radinovic' included in JavaDoc
I thought so too, but after quite some research I learned that this is never employed within any filter used by Spring / Spring-Security FilterChain.

Reason:
You don't want to interrupt the FilterChain itself, you need to continue it. By Adding a try...catch... finally you can corrupt the FilterChain, because you can catch an error from another filter within the Chain when you write a try...catch...finally around the
```java
chain.doFilter(request, response)
```

What's left are:
```java
HttpServletResponse r = (HttpServletResponse) response;
responses.set(r);
```

I decided to write it just like the filters of Spring core and spring security.
Don't add unneeded overhead for these two calls.

For reference look at 
> org.springframework.web.filter

Hope this is sufficient information to continue the PR.