Interfaced Workflows and GraftWorkflow

These workflows provide automatic input/output nodes generation, with some other utilities such as fast connection (avoiding to specify the connecting fields).

GraftWorkflow is intended to create evaluation workflows, where all the inputs are the same but several different methods are to be compared, stacking the outputs in lists.

![download](https://cloud.githubusercontent.com/assets/598470/3689885/fe7886b6-1343-11e4-89a6-810e74c09d9e.png)

Two additional interfaces have been coded: CollateInterface and MultipleSelectInterface. These interfaces multiplex/demultiplex outputs/inputs respectively.