Added some base classes for functional blocks

core/src/io/anuke/mindustry/entities/effect/Shield.java

@@ -0,0 +1,18 @@
+package io.anuke.mindustry.entities.effect;
+
+import io.anuke.ucore.entities.Entity;
+
+public class Shield extends Entity{
+	public boolean active;
+	//TODO
+	
+	@Override
+	public void added(){
+		active = true;
+	}
+	
+	@Override
+	public void removed(){
+		active = false;
+	}
+}