generic method for binding autocalculated annotation rows to the code that generates them

Automatically calculated annotation row objects need attributes that will allow the annotation generation code that generated them to be discovered and re-executed, should the alignment (or any other dependent data) be modified. Currently this is is achieved by hardwired annotation row names and a flag to indicate the row is autocalculated.

The implementation could be as simple as a plain-text field providing the fully qualified class name for the class implementing an 'annotation generator' interface. An additional parameter set attribute may also be needed to allow annotation generator specific settings to be stored along with the result, enabling the calculation to be repeated with new data.