Add "Import Voice"

[Dying-Ducks]

We have the "Export Voice" feature in the DemoManager which works exactly how it should.
But if it’s possible to extract the voice coms from the demo file, it should be possible to also insert voice coms into the demo file.

I know that a lot of people are looking for a way to connect external voice recordings (TeamSpeak, Discord, ...) to the demo file and if the demo manager could have a button to just "import voice" that would be a game changer.

I know there is the big issue of synchronization floating above all of this, but the ability to import recorded voice chat into demo itself would be a massive first step.

I don’t know how easy it is to implement (probably it’s more than just reverse the export protocol) or if it’s even possible, but it would be a huge feature.

I noticed that the exported voice files “only” contain the windows where the push-to-talk button was used (so no phases of silence in between). I don’t know if you filtered it out before exporting or it’s just how the voice chat is saved within the .dem file (every window with the associated tick where it started).