New RPC and daemon command to get output histogram

This is a list of existing output amounts along with the number
of outputs of that amount in the blockchain.

The daemon command takes:
- no parameters: all outputs with at least 3 instances
- one parameter: all outputs with at least that many instances
- two parameters: all outputs within that many instances

The default starts at 3 to avoid massive spamming of all dust
outputs in the blockchain, and is the current minimum mixin
requirement.

An optional vector of amounts may be passed, to request
histogram only for those outputs.

src/daemon/rpc_command_executor.cpp

@@ -1203,5 +1203,41 @@ bool t_rpc_command_executor::flush_txpool(const std::string &txid)
     return true;
 }
 
+bool t_rpc_command_executor::output_histogram(uint64_t min_count, uint64_t max_count)
+{
+    cryptonote::COMMAND_RPC_GET_OUTPUT_HISTOGRAM::request req;
+    cryptonote::COMMAND_RPC_GET_OUTPUT_HISTOGRAM::response res;
+    std::string fail_message = "Unsuccessful";
+    epee::json_rpc::error error_resp;
+
+    req.min_count = min_count;
+    req.max_count = max_count;
+
+    if (m_is_rpc)
+    {
+        if (!m_rpc_client->json_rpc_request(req, res, "get_output_histogram", fail_message.c_str()))
+        {
+            return true;
+        }
+    }
+    else
+    {
+        if (!m_rpc_server->on_get_output_histogram(req, res, error_resp))
+        {
+            tools::fail_msg_writer() << fail_message.c_str();
+            return true;
+        }
+    }
+
+    std::sort(res.histogram.begin(), res.histogram.end(),
+        [](const cryptonote::COMMAND_RPC_GET_OUTPUT_HISTOGRAM::entry &e1, const cryptonote::COMMAND_RPC_GET_OUTPUT_HISTOGRAM::entry &e2)->bool { return e1.instances < e2.instances; });
+    for (const auto &e: res.histogram)
+    {
+        tools::msg_writer() << e.instances << "  " << cryptonote::print_money(e.amount);
+    }
+
+    return true;
+}
+
 
 }// namespace daemonize