converting a CharmBrowser model instance to a Charm instance is duplicated

In subapps/browser/views/charm.js _addCharmEnvironment we convert a BrowserCharm into a Charm instance. That logic is duped in the charm-token.js widget in _addDraggability (it's actually passed the data for that from a View). This means there's two place to keep the logic on correcting the id and config ATTRS of the Charm model instance.

I'd suggest the Charm model instance gain a helper to initFromBrowserCharm(), or something along those lines) that can keep this mapping in one place and be reused for the drag-n-drop and manual deploy work.