Added a section about installing the Scala IDE Play2 plug-in

Please don't merge this for the moment becuase the image is not yet available.
I'll fix it as soon as we stage the Play2 plug-in.

Fix #54
Adds the play2 support install image
Merge pull request #55 from scala-ide/issue/add-play2-plugin-setup-in-play2-tutorial-54

Added a section about installing the Scala IDE Play2 plug-in