Refactor Eon -> Keyper set index

[blockchainluffy]

Places identified (not limited to these) are:

• identity registration and new keyper set events and corresponding tables
• decryption_key, decryption_key_share, current_decryption_trigger and decryption_signatures tables
• p2p msgs for DecryptionKeyShares and DecryptionKeys

Other than this refactor, one table name to be changed is
last_batch_config_sent -> last_batch_config_processed