Invalid proof of election in self-repair

[ghost]

What happened?

This issue happens when a node was running for quite some time, and then a new node joins the network.
When this new node tries to synchronize all the missing transactions, it throws errors saying the proof of election is invalid.

This is probably an issue with ordering of transactions

What is expected ?

When a node joins the network, it should download and synchronize transactions sequentially to ensure the consistency and the order of the transactions and in-memory states.

---

Epic: #321

[ghost]

Turns out, beacon summary aggregates contains transaction summaries which are after the summary time.
Which means others beacon summary for other time later will come, and the transactions will not be in the right order.

There is a chance the BeaconChain.get_full_beacon_summary is causing the issue.