couch: add identity view to get all keys

See merge request leap/webapp!61

Since the old keys used to be strings i started out by
json serializing the new keys with type, value, rev.

However storing serialized json in couch (json) does
not really make sense. So now we do not serialize but
instead have one json document. The lookup for a key of
type pgp may still return a string but for everything
that uses the new api it will return a hash with type
and revision.

This data structure is way easier to handle also on the
nickserver side.

subrepo:
  subdir:   "app/assets/javascripts/srp"
  merged:   "2088cbe"
upstream:
  origin:   "https://leap.se/git/srp_js"
  branch:   "master"
  commit:   "2088cbe"
git-subrepo:
  version:  "0.3.1"
  origin:   "https://github.com/ingydotnet/git-subrepo"
  commit:   "a7ee886"

This needs to be included in the platforms views.

We used to just ignore the key.
Also separated the code for handling key updates from other
user updates. This should eventually be moved to a different
route. Mixing the two makes the implementation really hard.

fixes #8796

Cleaned up UserController#update earlier but missed that it was
used to change fallback email addresses. Now it is back. This
time including an integration test.

we were simply referring to the wrong key.
includes test