"Set all faders to new client level" only affects current users

**Describe the bug**

When using "Set all faders to new client level" this only resets the faders of current users, if a previous user signs in it's level is still set to the previous level.

**To Reproduce**

Sign in to a server with multiple users.
Set all levels to i.e. max.
Sign out one user.
use "Set all faders to new client level".
sign in the previous user again and it's level will still be set to max. not the "New Client Level".

**Expected behavior**

Just like when using "Clear All Stored Solo and Mute Settings" also the stored levels should be reset to new client level when using "Set all faders to new client level"

**Screenshots**

**Operating system**

n.a.

**Version of Jamulus**

3.6.x, 3.7.0
**Additional context**

Maybe also an added option to delete all stored users?

Start by reproducing the described sequence with multiple users: change all faders, sign one user out, apply "Set all faders to new client level," and sign that user in again. Trace how current faders and stored user levels are handled, and consider the issue done when both current and returning users receive the new client level.

Written by the indexing model from the issue text.