identify: provide changectx to templater

formatter: proxy fm.context() through converter Otherwise nested template formatter would not see the context objects. It's just a boolean flag now. We might want to change it to 'ctxs -> items' function so changectx attributes are populated automatically in JSON, but I'm not sure.

identify: change p1/p2 to a list of parents It makes sense because the nested data structure is a list of items.