Adds support for checking the timestamp inherent while validating a block (#494)

* Adds support for checking the timestamp inherent while validating a block

This adds support for checking the timestamp inherent while validating a
block. This will use the relay chain slot number * relay chain slot
duration to calculate a timestamp. This timestamp is used to check the
timestamp in the timestamp inherent.

* Update polkadot-parachains/rococo-runtime/src/lib.rs

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

* Update polkadot-parachains/statemine-runtime/src/lib.rs

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

* Update primitives/timestamp/src/lib.rs

Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

* Fix warnings

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: André Silva <123550+andresilva@users.noreply.github.com>

client/collator/src/lib.rs

@@ -390,7 +390,7 @@ mod tests {
 
 	#[test]
 	fn collates_produces_a_block_and_storage_proof_does_not_contains_code() {
-		let _ = env_logger::try_init();
+		sp_tracing::try_init_simple();
 
 		let spawner = TaskExecutor::new();
 		let para_id = ParaId::from(100);