Make sure images get promoted for WorkshopIdea -> Workshop and StoryIdea -> Story

[maebeale]

Make sure images get promoted for WorkshopIdea -> Workshop and StoryIdea -> Story

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OLD NOTES:
WorkshopIdeas are submitted by Users, and may or may not become Workshops
We want admins to be able to "promote" a WorkshopIdea to a Workshop, via url params

Follow the pattern established by StoryIdea form -> Story form, so the same feature is available for WorkshopIdeas
(the pattern is essentially adding url params to the "Promote" button, which is a new_workshop_path button and the Workshop form needs to default to params sent or f.object values)

[jmilljr24]

#815