Fix getOnlinePlayers call to support all versions

Moved IPlayerDataManager from api module to common module - it is not part of the API as there is no supported way to obtain an instance of it.

internal/v1_7_R4/pom.xml

@@ -17,6 +17,12 @@
       <artifactId>openinvcommon</artifactId>
       <version>1.0-SNAPSHOT</version>
     </dependency>
+    <dependency>
+      <groupId>org.spigotmc</groupId>
+      <artifactId>spigot-api</artifactId>
+      <version>1.7.10-R0.1-snapshot</version>
+      <scope>provided</scope>
+    </dependency>
     <dependency>
       <groupId>org.bukkit</groupId>
       <artifactId>craftbukkit</artifactId>