Save last audio volume instead of setting a default in settings

[Salanto]

Right now AO2's volume in the settings is the clients default volume when joining a server. While running changes are made in the mixer.

This creates several issues:

• Many users are unaware that the audio settings in the menu/config are the default join volumes and wonder why their audio volumes from mixer don't carry over to the enxt time they open the client.
• It works different than WebAO, which saves your last audio settings and restores them when reopening it
• It is extremely counter-intuitive to be able to change a setting which does nothing until you rejoin a server.

A solution would be to remove the default audio volume behaviour and just save the last set volume from mixer/settings, allowing both to change volume and restore them from settings for a consistent experience.

[stonedDiscord]

web parity issue :omegalol:

[Salanto]

:omgparityissue: 😱 😱