Correct Substrate Tendermint start block

The Tendermint machine uses the passed in number as the block's being 
worked on number. Substrate passed in the already finalized block's 
number.

Also updates misc comments.

substrate/tendermint/client/src/import_queue.rs

@@ -1,4 +1,5 @@
 use std::{
+  convert::TryInto,
   pin::Pin,
   sync::{Arc, RwLock},
   task::{Poll, Context},
@@ -115,8 +116,8 @@ where
         0,
         (
           // Header::Number: TryInto<u64> doesn't implement Debug and can't be unwrapped
-          match best.try_into() {
-            Ok(best) => BlockNumber(best),
+          match TryInto::<u64>::try_into(best) {
+            Ok(best) => BlockNumber(best + 1),
             Err(_) => panic!("BlockNumber exceeded u64"),
           },
           Commit::<TendermintValidators<B, Be, C>>::decode(

substrate/tendermint/client/src/validators.rs

@@ -25,7 +25,7 @@ struct TendermintValidatorsStruct {
   weights: Vec<u64>,
 
   keys: Pair, // TODO: sp_keystore
-  lookup: Vec<Public>, // TODO: sessions
+  lookup: Vec<Public>,
 }
 
 impl TendermintValidatorsStruct {

substrate/tendermint/machine/src/lib.rs

@@ -157,7 +157,7 @@ impl<N: Network + 'static> TendermintMachine<N> {
   fn timeout(&self, step: Step) -> Instant {
     let mut round_time = Duration::from_secs(N::BLOCK_TIME.into());
     round_time *= self.round.0 + 1;
-    let step_time = round_time / 3;
+    let step_time = round_time / 3; // TODO: Non-uniform timeouts
 
     let offset = match step {
       Step::Propose => step_time,