Use milliseconds for timestamp resolution (#3210)

* node: tabify constants file

* node: define minimum period and slot duration in milliseconds

* core: srml: use milliseconds for timestamp resolution

* core: update slot_duration to millis in tests

* node: bump spec_version

* node: fix integration test

* node: fix executor test

* Update node/runtime/src/lib.rs

Co-Authored-By: Kian Peymani <Kianenigma@users.noreply.github.com>

* node: fix docs on timestamp resolution

* node: add docs on u64 for millis

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

@@ -150,10 +150,10 @@ impl indices::Trait for Runtime {
 }
 
 parameter_types! {
-	pub const MinimumPeriod: u64 = 5;
+	pub const MinimumPeriod: u64 = 5000;
 }
 impl timestamp::Trait for Runtime {
-	/// A timestamp: seconds since the unix epoch.
+	/// A timestamp: milliseconds since the unix epoch.
 	type Moment = u64;
 	type OnTimestampSet = Aura;
 	type MinimumPeriod = MinimumPeriod;