Unsafe public fields in UpdateInterface class: make public fields final

This commit makes the UpdateInterface class immutable. The Config -> UpdateInterface initialization is moved to the UpdateInterface constructor. Default values for the fields are moved to the constructor as well. Instances of String[] are changed to List<String> and made immutable. Instances of java.awt.Rectangle (which is mutable) are replaced with a new immutable com.threerings.getdown.util.Rectangle class.

Although java.awt.Color is (sort of) immutable, it was also removed and replaced with a new immutable com.threerings.getdown.util.Color class, since it was the last dependency from the getdown core module to anything in the java.awt package, which means that when we migrate to Java 9+ the core module should no longer require a dependency on the java.desktop module.

The assertions and expected values in ColorTest have been verified against the corresponding java.awt.Color values.

(Triggered by internal security audit and Fortify analysis.)

core/src/test/java/com/threerings/getdown/util/ColorTest.java

@@ -0,0 +1,111 @@
+//
+// Getdown - application installer, patcher and launcher
+// Copyright (C) 2004-2016 Getdown authors
+// https://github.com/threerings/getdown/blob/master/LICENSE
+
+package com.threerings.getdown.util;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+
+/**
+ * Tests {@link Color}.
+ */
+public class ColorTest
+{
+    @Test
+    public void testRgbConstructor ()
+    {
+        Color color1 = new Color(0, 0, 0);
+        assertEquals(0, color1.red);
+        assertEquals(0, color1.green);
+        assertEquals(0, color1.blue);
+        assertEquals(255, color1.alpha);
+        assertEquals(0xFF000000, color1.rgba());
+        assertEquals(0, color1.brightness(), 0.0000001);
+        assertEquals(Color.BLACK, color1);
+
+        Color color2 = new Color(255, 255, 255);
+        assertEquals(255, color2.red);
+        assertEquals(255, color2.green);
+        assertEquals(255, color2.blue);
+        assertEquals(255, color2.alpha);
+        assertEquals(0xFFFFFFFF, color2.rgba());
+        assertEquals(1, color2.brightness(), 0.0000001);
+        assertEquals(Color.WHITE, color2);
+
+        Color color3 = new Color(1, 2, 3);
+        assertEquals(1, color3.red);
+        assertEquals(2, color3.green);
+        assertEquals(3, color3.blue);
+        assertEquals(255, color3.alpha);
+        assertEquals(0xFF010203, color3.rgba());
+        assertEquals(0.0117647, color3.brightness(), 0.0000001);
+
+        Color color4 = new Color(-100, 300, 200);
+        assertEquals(0, color4.red);
+        assertEquals(255, color4.green);
+        assertEquals(200, color4.blue);
+        assertEquals(255, color4.alpha);
+        assertEquals(0xFF00FFC8, color4.rgba());
+        assertEquals(1, color4.brightness(), 0.0000001);
+    }
+
+    @Test
+    public void testRgbaConstructor ()
+    {
+        Color color1 = new Color(0, false);
+        assertEquals(0, color1.red);
+        assertEquals(0, color1.green);
+        assertEquals(0, color1.blue);
+        assertEquals(255, color1.alpha);
+        assertEquals(0xFF000000, color1.rgba());
+        assertEquals(0, color1.brightness(), 0.0000001);
+        assertEquals(Color.BLACK, color1);
+
+        Color color2 = new Color(0, true);
+        assertEquals(0, color2.red);
+        assertEquals(0, color2.green);
+        assertEquals(0, color2.blue);
+        assertEquals(0, color2.alpha);
+        assertEquals(0, color2.rgba());
+        assertEquals(0, color2.brightness(), 0.0000001);
+        assertFalse(Color.BLACK.equals(color2));
+
+        Color color3 = new Color(0x00FFFFFF, false);
+        assertEquals(255, color3.red);
+        assertEquals(255, color3.green);
+        assertEquals(255, color3.blue);
+        assertEquals(255, color3.alpha);
+        assertEquals(0xFFFFFFFF, color3.rgba());
+        assertEquals(1, color3.brightness(), 0.0000001);
+        assertEquals(Color.WHITE, color3);
+
+        Color color4 = new Color(0x00FFFFFF, true);
+        assertEquals(255, color4.red);
+        assertEquals(255, color4.green);
+        assertEquals(255, color4.blue);
+        assertEquals(0, color4.alpha);
+        assertEquals(0x00FFFFFF, color4.rgba());
+        assertEquals(1, color4.brightness(), 0.0000001);
+        assertFalse(Color.WHITE.equals(color4));
+
+        Color color5 = new Color(0x00010203, false);
+        assertEquals(1, color5.red);
+        assertEquals(2, color5.green);
+        assertEquals(3, color5.blue);
+        assertEquals(255, color5.alpha);
+        assertEquals(0xFF010203, color5.rgba());
+        assertEquals(0.0117647, color5.brightness(), 0.0000001);
+
+        Color color6 = new Color(0x00010203, true);
+        assertEquals(1, color6.red);
+        assertEquals(2, color6.green);
+        assertEquals(3, color6.blue);
+        assertEquals(0, color6.alpha);
+        assertEquals(0x00010203, color6.rgba());
+        assertEquals(0.0117647, color6.brightness(), 0.0000001);
+    }
+}