Add Menu Selection and Exit Sounds / Implement Unused Addon Menu Sounds

About as simple as the title.

The former adds in two new sound effects, menu2 and menu3, in order to prevent menu1 abuse. menu2 is the select sound in Knuckles Chaotix, while menu3 is a sound from Sonic 3K that was used for the same purpose in the ROM hack Sonic 3 Complete. I was originally going to use the starpost sound effect for menu2, but I changed it after realizing it was pretty annoying. Adding these two sounds also makes menu sound customization possible, so you could mod in the menu sounds from Sonic Heroes or something if you'd like.

As for the latter, I noticed the sounds adderr, notadd, and addfil in srb2.pk3 go completely unused. Based on their file name and placement in sounds.h and their captions in sounds.c, I figured that they were intended for the add-ons menu. So, why not ununuse them? And that's part of what this merge request does. However, I do understand they may not fit in as well with the rest of the menu sounds (which is probably why they went unused in the first place), so if you want me to revert this, I'd be more than willing to.

You will need this wad to test this request, and if it gets merged in, the two new menu sounds will need to be added into patch.pk3.