Implement real time statistic visualization (#16956)

Docs at https://trinitycore.atlassian.net/wiki/display/tc/Monitoring+a+TrinityCore+server

* Common/Graphs: Initial proof of concept

* Move influx db code to its own class

* Reuse the same socket

* Allow to log values of different categories

* Allow to log events

* Pass the timestamp to influxdb

* Send events in batches

* Send data async

* Log server shutdown.
Fix memory leak.

* Allow to enable/disable Stats in the settings and at runtime

* Read interval between each batch send from config

* Add InfluxDB connection info to configs

* Move each event category to its own table

* Log pathfinding queries

* Move categories table initialization to constructor using enum as key to avoid assigning the table name to the wrong enum value

* Log player login/logout events.
Pass the hostname correctly in the HTTP request.

* Fix linux build

* Handle "Connection: close" HTTP header, reconnecting on next scheduled send.
Disable StatsLogger if connection fails, logging the error.

* Add an enum for categories of logged values, it's still possible to pass a string instead of the enum.

* Don't log the whole batchedData when InfluxDB returns an error, it's too long and unreadable on console.

* Allow to call a function at a specified interval in thread-safe World::Update() context to log data like player count.

* Log map tile load/unload

* Core/StatsLogger: Allow logging more value types other than ints

https://docs.influxdata.com/influxdb/v0.10/write_protocols/write_syntax/

* Fix a typo in string escape of StatsLogger

* Yet more fixes to the escaping in FormatInfluxDBValue

* DB/Gameobject: Fix respawn time of few Quest GameObjects

By Tauriella, closes #16701

* DB/Misc: Fix some engrish

By tkrokli closes #16648

* Tools/MMaps: Add format library linking to mmaps_generator

(Very) partial cherry pick of ed75b0649a

* Core/StatsLogger: Simplify code

Convert values and categories arrays to maps initialized in-place
Remove constructor and destructor

* Core/StatsLogger: Add realm name to the event and value tags

* Log amount of processed packet of each session

* Apply recent singleton changes to sStatsLogger too

* Fix influxdb data format if no realm name is present

* Remove unneeded newlines from request body, fixes response 400 from InfluxDB 0.10

* Rename Reporting folder to Metric

* Rename StatsLogger to Metric

* Rename InfluxDB configs to Metric

* Add Grafana dashboards

* Add a random annoying macro

* Move string formatting to Metric::SendBatch(), reducing performance footprint of Metric::LogEvent() and Metric::LogValue()

* Update grafana graphs refresing tags on load and showing now-15m data, refreshing every minute. These settings can be modified in grafana.

* Rename MetricData fields

* Contrib/Grafana: Rename dashboard files

* Contrib/Grafana: Replace hardcoded Windows/Ubuntu realm names by the default, Trinity

* Config/Worldserver: Add missing section to the index

* Contrib/Grafana: Add singlestat panels with current online players, update diff averages (1 min, 5 mins and 15 mins)

http://i.imgur.com/Zi8lfvS.png

* Core/Metric: Replace the enums MetricEventCategory and MetricValueCategory by strings

For the sake of simplicity and less recompile time when adding new metrics, similar to how TC_LOG_* works

* Contrib/Grafana: Display the current number of online players and not its average

Closes #15075
(cherry picked from commit 3ae1016082)

# Conflicts:
#	src/server/game/Server/WorldSession.cpp
#	src/server/game/World/World.cpp
#	src/server/worldserver/Main.cpp

src/common/Collision/Maps/MapTree.cpp

@@ -22,6 +22,7 @@
 #include "VMapDefinitions.h"
 #include "Log.h"
 #include "Errors.h"
+#include "Metric.h"
 
 #include <string>
 #include <sstream>
@@ -415,6 +416,8 @@ namespace VMAP
         }
         else
             iLoadedTiles[packTileID(tileX, tileY)] = false;
+        TC_METRIC_EVENT("map_events", "LoadMapTile",
+            "Map: " + std::to_string(iMapID) + " TileX: " + std::to_string(tileX) + " TileY: " + std::to_string(tileY));
         return result;
     }
 
@@ -473,6 +476,8 @@ namespace VMAP
             }
         }
         iLoadedTiles.erase(tile);
+        TC_METRIC_EVENT("map_events", "UnloadMapTile",
+            "Map: " + std::to_string(iMapID) + " TileX: " + std::to_string(tileX) + " TileY: " + std::to_string(tileY));
     }
 
     void StaticMapTree::getModelInstances(ModelInstance* &models, uint32 &count)