Rewards and slashing, early-exit of bad sessions (#234)

* Recompile runtime.

* Introduce and enforce block time

* Introduce early session ending.

* Report most of staking module

* rewards, proper early exit and slashing

* Fix build & session logic, introduce tests

* Fixed staking tests.

* Initial test for reward

* Fix test

* Tests for slashing

* Update/fix preset configs

* Fix some tests.

* Fix some staking tests

* Minor fix

* minor cleanups

* Fix build

* Rename timestamp::Value -> Moment

* Require final block of session to be timely