Document more TODOs as tickets (#1418)

Went through the TODOs, removed a bunch, which are outdated or nothing more than a regular comment, documented a bunch more as actual tickets and made them FIXMEs and unified their structure (`FIXME #TICKETNO DESC` for local tickets, `FIXME: DESC LINK` for external tickets) for easier in-editor support. Further more remove unnecessary remarks and related old code that I noticed in that instance.

substrate/core/transaction-pool/src/api.rs

@@ -67,7 +67,6 @@ impl<T, Block> txpool::ChainApi for ChainApi<T, Block> where
 		Ok(self.client.runtime_api().validate_transaction(at, uxt)?)
 	}
 
-	// TODO [toDr] Use proper lbock number type
 	fn block_id_to_number(&self, at: &BlockId<Self::Block>) -> error::Result<Option<txpool::NumberFor<Self>>> {
 		Ok(self.client.block_number_from_id(at)?)
 	}