single mandatory root element in presentation tree

ensureDefinitionModel should be renamed. The `if else` clause in this function should not exist. We have two schemas of the report and here we try to handle them dynamically. If we were using Java, we would have a `Report` type and a `Report2` type and a function to migrate from `Report` to `Report2`.

I am not sure what is the status with jsound but by using typescript we would have a clear stable schema for the report and versioning for the different versions of the schema. Even if we do everything in Javascript the minset should be in terms of schema definition and versioning and we shouldn't do crazy dynamic stuff.