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/srml/timestamp/src/lib.rs

@@ -170,7 +170,7 @@ impl ProvideInherentData for InherentDataProvider {
 			.map_err(|_| {
 				"Current time is before unix epoch".into()
 			}).and_then(|d| {
-				let duration: InherentType = d.as_secs();
+				let duration: InherentType = d.as_millis() as u64;
 				inherent_data.put_data(INHERENT_IDENTIFIER, &duration)
 			})
 	}