Update Synchronizer (node) implementation

- node:
    - Extend config to add initial variables of the smart contracts used as
      defaults before they are changed via events.
    - In stopped channels, set size 1 so that panics are not witheld until the
      node stops completely.
- common:
    - In Smart Contract variables, comment:
      - `WDelayerVariables.HermezRollupAddress` because it's not needed.
      - `RollupVariables.Buckets` because there are no events for it, and for
        now it's not used.
- historydb:
    - Add functions to get and set smart contract variables.
- db:
    - Add `Rollback` function in `utils.go` to reduce boilerplate in sql
      transaction rollbacks in defers in db functions.
    - Update `rollup_vars` and `auction_vars` (renamed from `consensus_vars`)
      table, and add `wdelayer_vars` table.
- synchronizer:
    - Synchronize WDelayer
    - Handle SC variables properly
- test/ethclient:
    - Add essential implementation of WDelayer

cli/node/main.go

@@ -107,6 +107,7 @@ func getConfig(c *cli.Context) (*Config, error) {
 	if err != nil {
 		return nil, err
 	}
+	// nodeCfg.Synchronizer.InitialVariables.WDelayer.HermezRollupAddress = nodeCfg.SmartContracts.Rollup
 	cfg.node = nodeCfg
 
 	return &cfg, nil