A random beacon (#96)

* Completely rework dispatch mechanism into something modular.

Not yet complete but 75% there.

* Council vote tests.

* Fix tests.

* whitespace.

* Fix demo runtime tests.

* Fix up tests.

* Remove dead code.

* Initial util code for random beacon

* Timestamp uses new storage API.

* Move over system module to new API.

* Much nicer storage API, moved over staking module.

* More refactoring.

* Democracy uses new storage API.

* Council uses new RPC.

* Fix more tests.

* Use match for Id

* Generic mix.

* Integrate random beacon

* Update binaries.

* Fixes relating to with_ext removal.

* Remove dead code.

* Rework mixer into an iterator adaptor.

* Link to paper.

* Algorithm cleanups

* Merge and fix test.

* Docs.

* Fix typo.

* rename

* Fix tests.