Task-type Workflows Activities an also be set as startup task

[Piedone]

Describe the bug

You can set Task-type Activities as startup tasks on the workflow canvas. However, this doesn't make sense, since a Task can't start a workflow, only an Event can.

Orchard Core version

22fbbb4

To Reproduce

1. Add any Task like Notify to a workflow.
2. Notice that you can set it as a startup task.

Expected behavior

The startup task button only appears for events. Also, the terminology "startup task" is incorrect as well, since it should say "startup event".

Logs and screenshots

E.g. a Notify Task can't start a workflow, but you can set it as a startup task: