More comprehensive identity system (#4326)

* Initial prototype

* Work on test harness.

* Minor removal

* Add some tests

* Fix tests

* More tests

* Final tests

* General documentation

* Function-level docs.

* Function-level docs.

* Identity fields.

* Fix dependency

* Docs

* Spelling nits

* Address grumbles.

substrate/frame/nicks/Cargo.toml

@@ -15,7 +15,7 @@ system = { package = "frame-system", path = "../system", default-features = fals
 
 [dev-dependencies]
 primitives = { package = "sp-core",  path = "../../primitives/core" }
-balances = { package = "pallet-balances", path = "../balances", default-features = false }
+balances = { package = "pallet-balances", path = "../balances" }
 
 [features]
 default = ["std"]