gRPC support for account_tx and tx

- Add support for all transaction types and ledger object types to gRPC
  implementation of tx and account_tx.

- Create common handlers for tx and account_tx.

- Remove mutex and abort() from gRPC server. JobQueue is stopped before
  gRPC server, with all coroutines executed to completion, so no need for
  synchronization.

src/test/rpc/Submit_test.cpp

@@ -36,8 +36,8 @@ public:
     class SubmitClient : public GRPCTestClientBase
     {
     public:
-        rpc::v1::SubmitTransactionRequest request;
-        rpc::v1::SubmitTransactionResponse reply;
+        org::xrpl::rpc::v1::SubmitTransactionRequest request;
+        org::xrpl::rpc::v1::SubmitTransactionResponse reply;
 
         explicit SubmitClient(std::string const& port)
             : GRPCTestClientBase(port)