Split off System random functions into a new Randomness module (#3699)

* split off system randomness functions into a new module

* bump spec and impl version

* Move randomness to bottom of construct_runtime calls, move initialization into on_initialize

* Update srml/randomness/Cargo.toml

Co-Authored-By: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Update srml/randomness/src/lib.rs

Co-Authored-By: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Update srml/randomness/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update srml/randomness/Cargo.toml

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Improve system example

* Update Cargo.lock

* Fix randomness example

* Get rid of the stored index

* Add tests

* Add a random test

* Improve docs

* Fix executive test :^)

* Add a utility function to tests

* Update srml/randomness/Cargo.toml

Co-Authored-By: Gavin Wood <github@gavwood.com>

* Update srml/randomness/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update srml/randomness/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Change interpretation of block numbers

* rename crate

* refactor randomess module usage

* change random material len to a const

* Update srml/randomness-collective-flip/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Update srml/randomness-collective-flip/src/lib.rs

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/node-template/runtime/src/lib.rs

@@ -272,6 +272,7 @@ construct_runtime!(
 		Sudo: sudo,
 		// Used for the module template in `./template.rs`
 		TemplateModule: template::{Module, Call, Storage, Event<T>},
+		RandomnessCollectiveFlip: randomness_collective_flip::{Module, Call, Storage},
 	}
 );
 
@@ -340,7 +341,7 @@ impl_runtime_apis! {
 		}
 
 		fn random_seed() -> <Block as BlockT>::Hash {
-			System::random_seed()
+			RandomnessCollectiveFlip::random_seed()
 		}
 	}