Remove unused SHAMap::getItem
Add missing beast includes
Move nodestore to its own module
Tidy up includes:
* Replace boost with std equivalents:
  - bind, ref, cref, function, placeholders
* More "include what you use"
* Remove unnecessary includes
Remove ScopedPointer, ContainerDeletePolicy
Tidy up basics module:
* Move directory up
* Remove unity includes and "include what you use"
Ledger load and ledger replay fixes:
 * Stash the loaded ledger where consensus can find it.
 * When loading a ledger for startup, try the backend too
 * Apply replay transactions to a mutable snapshot