Update Form1.cs

to mute a non-default audio device instead of the default one. (to accomodate users changing their spotify audio device using the equalify plugin)

2 variables added,
soundDeviceOverride = boolean
overrideDevice = string

and an if-statement to handle the device override.

muting occurs using:
nircmd's 
mutesubunitvolume [Device Name] [Subunit Name] [mute mode]
or process specific,
muteappvolume [Process] [mute mode] {Device Name/Index}