add mouse button function to commandManager & OnScreenButton

Limelight/Input/CommandManager.swift

@@ -51,6 +51,12 @@ import UIKit
 @objc public class CommandManager: NSObject {
     @objc public static let shared = CommandManager()
     
+    @objc public static let mouseButtonMappings: [String: Int32] = ["M_LEFT" : BUTTON_LEFT,
+                                                       "M_MIDDLE" : BUTTON_RIGHT,
+                                                       "M_RIGHT" : BUTTON_RIGHT,
+                                                       "M_X1" : BUTTON_X1,
+                                                       "M_X2" : BUTTON_X2]
+
     static let keyMappings: [String: Int16] = [
         // Windows Key Codes
         "CTRL": 0x11,        // VK_CONTROL