Generic ICellInventoryHandler (#3624)

Allows addons who register a custom IStorageChannel to use the IStorageCell interface without registering a cell handler. Also adds some helpers (poweredInsert/poweredExtract).
This breaks API!

src/main/java/appeng/me/storage/MEInventoryHandler.java

@@ -129,7 +129,7 @@ public class MEInventoryHandler<T extends IAEStack<T>> implements IMEInventoryHa
 	}
 
 	@Override
-	public IStorageChannel getChannel()
+	public IStorageChannel<T> getChannel()
 	{
 		return this.internal.getChannel();
 	}