Added MouseButtons interface

src/model/MouseButtons.java

+package model;
+
+public interface MouseButtons {
+    int LEFTDOWN = 0x0002;
+    int LEFTUP = 0x0004;
+    int RIGHTDOWN = 0x0008;
+    int RIGHTUP = 0x0010;
+    int MIDDLEDOWN = 0x0020;
+    int MIDDLEUP = 0x0040;
+    int XDOWN = 0x0080;
+    int XUP = 0x0100;
+    int XBUTTON1 = 0x0001;
+    int XBUTTON2 = 0x0002;
+
+    static int getDown(int id) {
+        if (id < 1 || id > 6 || id == 3)
+            return -1;
+
+        switch (id) {
+            case 1:
+                return LEFTDOWN;
+            case 2:
+                return RIGHTDOWN;
+            case 4:
+                return MIDDLEDOWN;
+            case 5:
+            case 6:
+                return XDOWN;
+            default:
+                throw new IllegalStateException("Impossible case reached.");
+        }
+    }
+
+    static int getUp(int id) {
+        if (id < 1 || id > 6 || id == 3)
+            return -1;
+
+        switch (id) {
+            case 1:
+                return LEFTUP;
+            case 2:
+                return RIGHTUP;
+            case 4:
+                return MIDDLEUP;
+            case 5:
+            case 6:
+                return XUP;
+            default:
+                throw new IllegalStateException("Impossible case reached.");
+        }
+    }
+
+    static int getXButton(int id) {
+        if (id == 5) {
+            return XBUTTON1;
+        }
+        else if (id == 6) {
+            return XBUTTON2;
+        }
+        else {
+            return -1;
+        }
+    }
+}