LevelBuilder support for play lab

[Finishes: #79639696, #79639780, #79639834, #79639722]
1. This information for Studio-specific attributes should probably come from somewhere in the Studio model class rather than from the general-purpose levels controller.
2. You can specify a multiline string in ruby using the [here doc syntax](http://ruby-doc.org/docs/ruby-doc-bundle/Manual/man-1.4/syntax.html#here_doc) which might be useful here.