Update coordinator to work better under real net

- cli / node
    - Update handler of SIGINT so that after 3 SIGINTs, the process terminates
      unconditionally
- coordinator
    - Store stats without pointer
    - In all functions that send a variable via channel, check for context done
      to avoid deadlock (due to no process reading from the channel, which has
      no queue) when the node is stopped.
    - Abstract `canForge` so that it can be used outside of the `Coordinator`
    - In `canForge` check the blockNumber in current and next slot.
    - Update tests due to smart contract changes in slot handling, and minimum
      bid defaults
    - TxManager
        - Add consts, vars and stats to allow evaluating `canForge`
        - Add `canForge` method (not used yet)
        - Store batch and nonces status (last success and last pending)
        - Track nonces internally instead of relying on the ethereum node (this
          is required to work with ganache when there are pending txs)
        - Handle the (common) case of the receipt not being found after the tx
          is sent.
        - Don't start the main loop until we get an initial messae fo the stats
          and vars (so that in the loop the stats and vars are set to
          synchronizer values)
- eth / ethereum client
    - Add necessary methods to create the auth object for transactions manually
      so that we can set the nonce, gas price, gas limit, etc manually
    - Update `RollupForgeBatch` to take an auth object as input (so that the
      coordinator can set parameters manually)
- synchronizer
    - In stats, add `NextSlot`

cli/node/main.go

@@ -119,10 +119,17 @@ func cmdRun(c *cli.Context) error {
 	// catch ^C to send the stop signal
 	ossig := make(chan os.Signal, 1)
 	signal.Notify(ossig, os.Interrupt)
+	const forceStopCount = 3
 	go func() {
+		n := 0
 		for sig := range ossig {
 			if sig == os.Interrupt {
+				log.Info("Received Interrupt Signal")
 				stopCh <- nil
+				n++
+				if n == forceStopCount {
+					log.Fatalf("Received %v Interrupt Signals", forceStopCount)
+				}
 			}
 		}
 	}()