Add application call accounts to txn_participation table

[tolikzinovyev]

Subject of the issue

We currently add the following to the txn_participation table: sender, receiver, close address, asset sender, asset receiver, asset close address, freeze account. However, we are missing Transaction.ApplicationCallTxnFields.Accounts which are the accounts referenced in an application call. In the future, we might want to construct queries that need this information (e.g., get app call transactions that reference a particular address).

[gmalouf]

@winder I remember us discussing storing inner transactions at the same level as outer ones to facilitate searches (with appropriate ref txids, table separation, etc). Did that work ever end up finishing or was it paused?

[winder]

@winder I remember us discussing storing inner transactions at the same level as outer ones to facilitate searches (with appropriate ref txids, table separation, etc). Did that work ever end up finishing or was it paused?

@gmalouf Yes, that work was finished. It's not really related to this issue though.