couch: add identity view to get all keys

This needs to be included in the platforms views.

app/designs/identity/keys_by_email.js

+function(doc) {
+  if (doc.type != 'Identity') {
+    return;
+  }
+  if (typeof doc.keys === "object") {
+    emit(doc.address, doc.keys);
+  }
+}