Add support for "boundaries" to Gating-ML 2.0 transforms

Gating-ML 2.0 is being updated to include support for "bounded" transformations, see http://flowcyt.sf.net/gating/latest.pdf for details. It is pretty trivial. In summary, these transformations have two additional optional parameters: boundMin and boundMax. If the result of the defining function is less than boundMin, then the result of the transform is boundMin. Analogically, if the result of the defining function is more than boundMax, then the result of the transform is boundMax. 

I am implementing appropriate support for this in flowUtils, but need to extend flowCore accordingly as well. It is all fully backwards compatible and there are unit tests in flowUtils that make sure that this is working fine. Let me know if there are any concerns.

Thanks, 
Josef