Complex widgets are not cleared upon data submission, potentially resulting in misinputs.

[hstaige]

Currently, any widget that has sub-widgets (Transitions with upper and lower levels, PreviousData with the list of checkboxes), is not cleared upon submitting data regardless of whether or not the keep box is selected. This can result in users accidentally contaminating future submissions with the data from the last submission. Each widget creator should define a .clear method that handles getting rid of the data in a way the user expects.