Added a way to provide a complete spring context to jersey-spring

Hello Jersey,

Here is a small pull request that adds a way to load the spring context out of jersey-spring and pass it directly to the SpringComponentProvider.
I also wrote a little example application that uses this new feature to test a jersey controller with jersey test.

I love the framework but I also love spring and particularly spring-boot.
Jersey-spring is great but it is lacking a way to provide an annotated spring configuration when you are not in a servlet environment  (like when you test with jersey-test).

I blogged about a way to do so a few days ago : http://geowarin.github.io/spring-boot/jersey/2014/01/31/a-simple-spring-boot-and-jersey-application.html. In the article that shows how to integrate spring boot and jersey, I override SpringComponentProvider which is obviously a very bad way of doing things.

With spring going 4.0.0 and letting good old xml configs behind. I really feel this feature should be integrated to Jersey.
Please take your time to review the code and let me know if I can help you further.

Thanks