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

Builds/CMake/RippleConfig.cmake

@@ -21,7 +21,6 @@ find_dependency (Boost 1.70
     filesystem
     program_options
     regex
-    serialization
     system
     thread)
 #[=========================================================[

Builds/CMake/RippledCore.cmake

@@ -513,6 +513,7 @@ target_sources (rippled PRIVATE
   src/ripple/nodestore/impl/ManagerImp.cpp
   src/ripple/nodestore/impl/NodeObject.cpp
   src/ripple/nodestore/impl/Shard.cpp
+  src/ripple/nodestore/impl/TaskQueue.cpp
   #[===============================[
      main sources:
        subdir: overlay

Builds/CMake/RippledInterface.cmake

@@ -21,9 +21,7 @@ target_compile_definitions (opts
     >
     $<$<BOOL:${beast_no_unit_test_inline}>:BEAST_NO_UNIT_TEST_INLINE=1>
     $<$<BOOL:${beast_disable_autolink}>:BEAST_DONT_AUTOLINK_TO_WIN32_LIBRARIES=1>
-    $<$<BOOL:${single_io_service_thread}>:RIPPLE_SINGLE_IO_SERVICE_THREAD=1>
-    # doesn't currently compile ? :
-    $<$<BOOL:${verify_nodeobject_keys}>:RIPPLE_VERIFY_NODEOBJECT_KEYS=1>)
+    $<$<BOOL:${single_io_service_thread}>:RIPPLE_SINGLE_IO_SERVICE_THREAD=1>)
 target_compile_options (opts
   INTERFACE
     $<$<AND:$<BOOL:${is_gcc}>,$<COMPILE_LANGUAGE:CXX>>:-Wsuggest-override>

Builds/CMake/RippledSettings.cmake

@@ -100,12 +100,6 @@ option (have_package_container
 option (beast_no_unit_test_inline
   "Prevents unit test definitions from being inserted into global table"
   OFF)
-# NOTE - THIS OPTION CURRENTLY DOES NOT COMPILE :
-# TODO: fix or remove
-option (verify_nodeobject_keys
-  "This verifies that the hash of node objects matches the payload. \
-  This check is expensive - use with caution."
-  OFF)
 option (single_io_service_thread
   "Restricts the number of threads calling io_service::run to one. \
   This can be useful when debugging."

Builds/CMake/deps/Boost.cmake

@@ -47,7 +47,6 @@ find_package (Boost 1.70 REQUIRED
     filesystem
     program_options
     regex
-    serialization
     system
     thread)
 
@@ -69,7 +68,6 @@ target_link_libraries (ripple_boost
     Boost::filesystem
     Boost::program_options
     Boost::regex
-    Boost::serialization
     Boost::system
     Boost::thread)
 if (Boost_COMPILER)