Removed AEApi

Moved all internal access to the internal `Api` class using a new static
getter.

src/main/java/appeng/core/Api.java

@@ -18,6 +18,7 @@
 
 package appeng.core;
 
+import appeng.api.AEAddon;
 import appeng.api.IAppEngApi;
 import appeng.api.features.IRegistryContainer;
 import appeng.api.networking.IGridHelper;
@@ -31,8 +32,26 @@ import appeng.core.features.registries.PartModels;
 import appeng.core.features.registries.RegistryContainer;
 
 public final class Api implements IAppEngApi {
+
+    /**
+     * While permitting public access, directly using {@link Api#instance()} is not
+     * recommended except in very special cases.
+     */
     public static final Api INSTANCE = new Api();
 
+    /**
+     * Use primarily to access the API.
+     * 
+     * Using {@link IAppEngApi} intentionally to avoid using functionality not
+     * exposed by accident.
+     * 
+     * In some cases we might have to access the API before it is announced via
+     * {@link AEAddon}, otherwise we could just inject it into AE2 itself.
+     */
+    public static IAppEngApi instance() {
+        return INSTANCE;
+    }
+
     private final ApiPart partHelper;
 
     // private MovableTileRegistry MovableRegistry = new MovableTileRegistry();