Update bStats Metrics to 2.2.1.

The previously nested classes are now standalone, so imports and super
class definitions of the custom various charts are updated as well.

pom.xml

@@ -77,12 +77,6 @@
       <url>https://hub.spigotmc.org/nexus/content/groups/public/</url>
     </repository>
 
-    <!-- bStats repo -->
-    <repository>
-      <id>bstats-repo</id>
-      <url>http://repo.codemc.org/repository/maven-public/</url>
-    </repository>
-
     <!-- JitPack for Vault -->
     <repository>
       <id>jitpack.io</id>
@@ -111,7 +105,7 @@
     <dependency>
       <groupId>org.bstats</groupId>
       <artifactId>bstats-bukkit</artifactId>
-      <version>1.7</version>
+      <version>2.2.1</version>
       <scope>compile</scope>
     </dependency>