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.

pom.xml

@@ -27,6 +27,13 @@
       <version>1.7.31</version>
     </dependency>
 
+    <!-- https://bstats.org/getting-started/include-metrics -->
+    <dependency>
+      <groupId>org.bstats</groupId>
+      <artifactId>bstats-bukkit</artifactId>
+      <version>2.2.1</version>
+    </dependency>
+
     <!-- https://hub.spigotmc.org/nexus/content/groups/public/org/bukkit/bukkit/ -->
     <dependency>
       <groupId>org.bukkit</groupId>
@@ -175,6 +182,10 @@
               <minimizeJar>true</minimizeJar>
               <createDependencyReducedPom>false</createDependencyReducedPom>
               <relocations>
+                <relocation>
+                  <pattern>org.bstats</pattern>
+                  <shadedPattern>org.mobarena.stats.libs.bstats</shadedPattern>
+                </relocation>
                 <relocation>
                   <pattern>org.jdbi</pattern>
                   <shadedPattern>org.mobarena.stats.libs.jdbi</shadedPattern>