Fix account_tx sluggishness

[WietseWind]

Implements fix as per XRPLF/rippled@2e9261cb

• Pre fix: ignoring index, doing full table scan. Problematic on accounts with many records / large DB (FH server).

As per Ripple Eng:

The SQLite db is not using indexes with the previous SQL, so full table scan was going on. The fh nodes has a big table so the thread is hanging
I found the issue but it’s the developer who found the SQLite optimizer problem
It only happens when the account has a lot of transactions and marker is used for paging

[WietseWind]

Already merged into jshooks; - will reach DEV branch that way too.
#330