[Feat]: Pivotal Importer, Epics should be put into an In Progress or Done State based on Stories

[semperos]

The Pivotal Importer recipe already creates Epics from Pivotal Tracker epics, but it sets all of them to an Unstarted state. Using the states of constituent Stories in the given Epic would be an improvement:

• No Stories ➡️ Unstarted Epic
• All unstarted Stories ➡️ Unstarted Epic
• Some (but not all) started Stories ➡️ In Progress Epic
• All completed Stories ➡️ Completed Epic