Better support of transformations in the API

In the client UI you can insert several transformations. However when you need to apply transformations via the API you are much more limited. Only the pivot and unpivot transformations are well supported. For other transformations like add column, remove column, change column etc. you need the general "ExpressionTransformation". One major drawback is also that the ExpressionTransformation does not add any information to the Source Information in the Data Table Properties, so you are not aware what was done to the data table. Therefore please support the transformations available in the UI in the same way in the API!