[FEATURE] Balances|Trustlines: Return ledger_index, use last validated ledger by default (RLJS-127)

Also, returns `validated` key as a boolean (from the rippled response)
Is it possible that the regex is incorrect?

In the schema file for UINT32:

```
^$|^(429496729[0-5]|42949672[0-8][0-
```

That first case is checking for an empty string. @emschwartz do you remember where that schema came from? It comes from cd45dd7