Pulls/fix multiple dialogs

Couple of minor bug fixes.

8b107e6 - Group permission were not being applied to transitions available in the next actions dropdown.

95b9566 - To reproduce this issue. Select an existing workflow definition from the Workflows gridfield. Select the edit button on a transition to bring up the dialog editor. Action, Next action, Type dropdowns are present. Click Workflows from the left nav to get back to /admin/workflows. Select the same workflow definition as before and again click the edit button to display the dialog. Note the Action, Next action, and Type dropdowns are missing. This is because each time a new WorkflowField is created, a new dialog is also created, and in turn, another editor form. The dropdown fields in these editor form have the same id attribute so Chosen tries to apply dropdown behaviour to the first field matching the id. Which on subsequent visits to the workflow definition, is the incorrect form. The fix is to remove the dialog when leaving the view.