allow custom slot jei check and fix fluid color in cell workbanch (#401)

src/main/java/appeng/container/slot/IJEITargetSlot.java

@@ -1,4 +1,9 @@
 package appeng.container.slot;
 
 public interface IJEITargetSlot {
+
+    default boolean needAccept() {
+        return false;
+    }
+
 }