Added Hotkey class

src/model/Hotkey.java

+package model;
+
+import java.io.Serializable;
+
+public class Hotkey {
+    /**
+     * Virtual keycode of the hotkey.
+     */
+    protected final int keyCode;
+
+    /**
+     * Unique ID of the hotkey.
+     */
+    protected final int id;
+
+    /**
+     * Modifier for the hotkey.
+     */
+    protected final Modifier modifier;
+
+    /**
+     * Constructs an immutable hotkey.
+     * @param keyCode The virtual keycode of the hotkey.
+     * @param id The unique ID of the hotkey.
+     * @param modifier The modifier of the hotkey.
+     */
+    public Hotkey(int keyCode, int id, Modifier modifier) {
+        this.keyCode = keyCode;
+        this.id = id;
+        this.modifier = modifier;
+    }
+
+    /**
+     * Gets the Hotkeys virtual keyCode.
+     */
+    public int getKeyCode() {
+        return keyCode;
+    }
+
+    /**
+     * Gets the hotkey's unique ID.
+     */
+    public int getID() {
+        return id;
+    }
+
+    /**
+     * Get's the hotkey's modifier.
+     */
+    public Modifier getModifier() {
+        return modifier;
+    }
+}