Fix tuning plugin

[XiaoMigros]

Resolves: #28573
Resolves: #25720

Old:

New:

I took the liberty of combining all the tuning plugins into one, since they all do the same thing. Hoping this plugin isn't plagued with as many crashes as Retrograde, since the score modifications are less complicated!
Additionally, the plugin now works for list selections, has a reset option, and stores all the tunings in settings, instead of single tunings to a file.

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• Each commit's message describes its purpose and effects, and references the issue it resolves
• If changes are extensive, there is a sequence of easily reviewable commits
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• The code compiles and runs on my machine, preferably after each commit individually
• I created a unit test or vtest to verify the changes I made (if applicable)

[cbjeukendrup]

Someone else did something similar in #26257 😬
Hopefully both efforts can somehow be combined, but I fear that might be difficult...

[XiaoMigros]

That's very unfortunate! I'll leave it to you to decide which PR you want to go with, but I'm sure some parts of either could be combined...