The distinction between refs.Identity and refs.Feed should probaly go away

[boreq]

Right now we have two types refs.Identity and refs.Feed. This is quite confusing and at this development stage it is unclear what the difference between those types is. If we treat the Protocol Guide as our domain then there should probably be no distinction between those types. The existence of identity.Public makes it even more confusing. Until there is a clear reason to distinguish between those two type (eg. maybe after adding metafeeds/other feed formats) it may be the best to just stick to refs.Feed.