Improve shard concurrency:

* Reduce lock scope on all public functions
* Use TaskQueue to process shard finalization in separate thread
* Store shard last ledger hash and other info in backend
* Use temp SQLite DB versus control file when acquiring
* Remove boost serialization from cmake files

src/ripple/nodestore/impl/DatabaseNodeImp.cpp

@@ -28,9 +28,6 @@ void
 DatabaseNodeImp::store(NodeObjectType type, Blob&& data,
     uint256 const& hash, std::uint32_t seq)
 {
-#if RIPPLE_VERIFY_NODEOBJECT_KEYS
-    assert(hash == sha512Hash(makeSlice(data)));
-#endif
     auto nObj = NodeObject::createObject(type, std::move(data), hash);
     pCache_->canonicalize(hash, nObj, true);
     backend_->store(nObj);