Refactor string-to-integer conversions
Cleanups:
* Remove obsolete config variables
* Reduce coupling
* Use C++11 ownership containers
* Reduce use of naked pointers and prefer references over pointers
* Use auto when it makes sense
* Detect edge-case in unit tests
* Reduce the number of LedgerEntrySet public memberse
Add ledger cleaner documentation (RIPD-555)