[ODROID Go] Show current volume in menu and remember last set volume when starting a ROM

[shockdesign]

Is your feature request related to a problem? Please describe.
Right now it seems to always launch the game with the volume set as minimum, meaning you need to adjust the volume a few times in order to mute it.

Describe the solution you'd like
Show what the current volume is set to on the menu. And also make sure that when a ROM is launched it is set to the currently selected volume level.

Describe alternatives you've considered
Only alternative right now is to manually adjust the volume by pressing the adjust volume button multiple times in order to mute it as soon as the game starts. I assume this isn't an actual problem with the ESP32 board due to having a physical volume rocker? However on an ODROID Go device it's just a button which sets the volume one of 4 levels (including mute).

[Cralex]

This is a must-have feature for me before I switch my OdroidGo to this firmware. I tend to play with the volume muted and I would like to be able to leave it that way until I decide to unmute it.

[32teeth]

Enhancement for Issue #24