Added services manager framework. Services are interfaces that specifies capabilities to be implemented by providers. Example services include economy, <insert example 2>, etc.

src/main/java/org/bukkit/plugin/ServicePriority.java

@@ -0,0 +1,12 @@
+package org.bukkit.plugin;
+
+/**
+ * Represents various priorities of a provider.
+ */
+public enum ServicePriority {
+    Lowest,
+    Low,
+    Normal,
+    High,
+    Highest
+}