* Brings the soci subtree into rippled.
* Validator, peerfinder, and SHAMapStore use new soci backend.
* Optional postgresql backend for soci (if POSTGRESQL_ROOT env var is set).
The NuDB database backend is a high performance key/value store presented
as an alternative to RocksDB on Mac and Linux deployments, and the preferred
backend option for Windows deployments. The LevelDB backend is deprecated for
all platforms.
This includes these changes:
* Add Backend::verify API for doing consistency checks
* Add Database::close so caller can catch exceptions
* Improved Timing test for NodeStore creates a simulated workload
* Rename unity files
* Move some modules to new subdirectories
* Remove obsolete Visual Studio project files
* Remove obsolete coding style and TODO list