move code in src/Ledger to use proper sql wrapper instead of legacy sql wrapper

[MonsieurNicolas]

old wrappers are encouraging the use of raw SQL instead of using binding, which is error prone and can lead to failed queries or SQL injections.

Legacy in that case means:
src/ripple_app/data/SqliteDatabase.cpp ( SqliteDatabase and SqliteStatement)

it seems that beast:sqdb does what we want, we should standardize on it.

[jedmccaleb]

If we are going to use this please pull it out of beast. We will hopefully drop beast at some point.

[vinniefalco]

Or use the original, which supports different backends (like MySQL or Oracle)
http://soci.sourceforge.net/
beast is a much needed interface "firewall": rippled calls into beast, but not the other way around. This facilitates levelization:
http://www2.caret.cam.ac.uk/rsfwiki/Wiki.jsp?page=Levelization
This follows the principles in the Lakos' book:
"Large-Scale C++ Software Design"
http://www.amazon.com/gp/product/0201633620/002-7417214-8818440

[vinniefalco]

More about beast:
https://stellartalk.org/topic/6464-beast-a-useful-library-and-api-firewall-to-assist-levelization/