Fluid cleanup and performance improvements (#3581)

Use custom gui widget with custom synchronization for rendering fake fluid slots.

src/main/java/appeng/fluids/util/IAEFluidInventory.java

@@ -0,0 +1,26 @@
+/*
+ * This file is part of Applied Energistics 2.
+ * Copyright (c) 2013 - 2018, AlgorithmX2, All rights reserved.
+ *
+ * Applied Energistics 2 is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Applied Energistics 2 is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with Applied Energistics 2.  If not, see <http://www.gnu.org/licenses/lgpl>.
+ */
+
+package appeng.fluids.util;
+
+
+@FunctionalInterface
+public interface IAEFluidInventory
+{
+	void onFluidInventoryChanged( final IAEFluidTank inv, final int slot );
+}