Add normalized script and sounds discussion

Hi I'm not sure if there is interest in this but I figured I would check in. I use your xdg-sound-theme on postmarketOS running on a Pinephone Pro and frequently notice that the phone-incoming-call sound is much more audible than the message-new-instant sound, which is very quiet. For my application, running on my phone, I was constantly not hearing text messages, which led to me investigating why and coming up with this solution.

I made a script that finds the loudest sound file in the current group and normalizes the max volume of each sound so that they all have the same max volume.

Here I've attached a screenshot showing the waveform for phone-incoming-call on top, the current message-new-instant on the bottom left, and the normalized message-new-instant on the bottom-right. To my ears the new files sound much better and more consistent.

So I realize that this MR is a bit of a mess, but I just wanted to check in and see if there is interest in accepting the new files, and if there is such interest I'd be happy to work with you to get this MR in good shape.

Thanks!