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

synchronizer/synchronizer_test.go

@@ -241,6 +241,11 @@ func TestSync(t *testing.T) {
 			Auction:  1,
 			WDelayer: 1,
 		},
+		InitialVariables: SCVariables{
+			Rollup:   *clientSetup.RollupVariables,
+			Auction:  *clientSetup.AuctionVariables,
+			WDelayer: *clientSetup.WDelayerVariables,
+		},
 	})
 	require.Nil(t, err)