Refactor epoch changes to a separate crate (#4785)

* Init epoch changes module

* Initial integration of new epoch changes module for BABE

* Fix all initial compile errors

* rename: digest -> digests

* Fix babe tests

* Bump impl_version

* Fix more test issues

* Remove test flag for tree

It unfortunately won't work for multiple crates.

* Update cargo lock

* Fix duplicate parking_lot version

* Add missing license header

substrate/Cargo.toml

@@ -25,8 +25,9 @@ members = [
 	"client/consensus/babe",
 	"client/consensus/manual-seal",
 	"client/consensus/pow",
-	"client/consensus/slots",
 	"client/consensus/uncles",
+	"client/consensus/slots",
+	"client/consensus/epochs",
 	"client/db",
 	"client/executor",
 	"client/executor/common",