#1420 Fader Settings improvements

[pljones]

Short description of changes

Two changes relating to #1420:

• Edit -> Set All Faders to New Client Level
  This retained the last known level for any client, so when that client rejoined the server, their old level was restored
  
  This has been reworded to make its behaviour clear
  
  "Set Current Faders to New Client Level" will be the behaviour that is intended - it will not take any stored fader levels into account. (Of course, these fader levels will then apply should a "current" client leave and rejoin.)

• Edit -> Stored Fader Settings
  This new sub-menu replaces "Clear All Stored Solo and Mute Settings" and finer-grained control, including allowing all settings to be purged:
  
  

CHANGELOG: Client: Fader Settings improvements

Context: Fixes an issue?

Fixes: -1420

Does this change need documentation? What needs to be documented and how?

Yes!

• App translations are affected
• Site documentation is affected

Status of this Pull Request

It runs and looks okay. I don't generally worry about stored fader settings, so I've not got much to test on. It could do with several people who use the feature heavily looking at it.

@pgScorpio, hopefully this is what you were after.

What is missing until this pull request can be merged?

• Code review.
• More testing by people who use the feature.
• Usability feedback.

Checklist

• I've verified that this Pull Request follows the general code principles
• I tested my code and it does what I want
• My code follows the style guide
• I waited some time after this Pull Request was opened and all GitHub checks completed without errors.
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