Only first indexation works

Because subscribeNewBlock only indexes the last finalized block, and forget all the previous since our last indexation.

For example we have:

• first indexation: indexes blocks up to #1000
• finalization event at #1500: indexes only block #1500 (forgetting about blocks [1001;1499]
• finalization event at #2000: indexes only block #2000 (forgetting about blocks [1501;1999]
• etc