Add bStats metrics.

Introduces the bStats metrics library to the plugin. This first commit
contains just a single custom chart, the `store_type`, which will help
figure out which stores to focus on for performance optimization and
such.

src/main/java/org/mobarena/stats/MobArenaStatsPlugin.java

@@ -2,6 +2,7 @@ package org.mobarena.stats;
 
 import com.garbagemule.MobArena.MobArena;
 import com.garbagemule.MobArena.commands.CommandHandler;
+import org.bstats.bukkit.Metrics;
 import org.bukkit.command.PluginCommand;
 import org.bukkit.configuration.ConfigurationSection;
 import org.bukkit.event.HandlerList;
@@ -12,6 +13,7 @@ import org.mobarena.stats.command.ExportCommand;
 import org.mobarena.stats.command.GlobalStatsCommand;
 import org.mobarena.stats.command.ImportCommand;
 import org.mobarena.stats.command.PlayerStatsCommand;
+import org.mobarena.stats.metrics.StoreTypeChart;
 import org.mobarena.stats.platform.AsyncBukkitExecutor;
 import org.mobarena.stats.platform.SyncBukkitExecutor;
 import org.mobarena.stats.session.SessionListener;
@@ -79,6 +81,7 @@ public class MobArenaStatsPlugin extends JavaPlugin implements MobArenaStats {
             createConfigFile();
             setupExecutors();
             setupCommands();
+            setupMetrics();
         } catch (Exception up) {
             // If setup fails, we can't recover, so throw up
             throw new RuntimeException(up);
@@ -131,6 +134,11 @@ public class MobArenaStatsPlugin extends JavaPlugin implements MobArenaStats {
         handler.register(ImportCommand.class);
     }
 
+    private void setupMetrics() {
+        Metrics metrics = new Metrics(this, 11932);
+        metrics.addCustomChart(new StoreTypeChart(this));
+    }
+
     private void reload() {
         try {
             createSessionStore();

src/main/java/org/mobarena/stats/metrics/StoreTypeChart.java

@@ -0,0 +1,27 @@
+package org.mobarena.stats.metrics;
+
+import org.bstats.charts.SimplePie;
+import org.bukkit.configuration.Configuration;
+import org.bukkit.configuration.ConfigurationSection;
+import org.mobarena.stats.MobArenaStatsPlugin;
+import org.mobarena.stats.store.StatsStore;
+
+public class StoreTypeChart extends SimplePie {
+
+    public StoreTypeChart(MobArenaStatsPlugin plugin) {
+        super("store_type", () -> {
+            StatsStore store = plugin.getStatsStore();
+            if (store == null) {
+                return null;
+            }
+
+            // If the store isn't null, it means whatever type is set in
+            // the config-file is valid and has already been parsed, so
+            // we can just extract and submit it.
+            Configuration config = plugin.getConfig();
+            ConfigurationSection section = config.getConfigurationSection("store");
+            return section.getString("type");
+        });
+    }
+
+}