improve FX Select buttons mapping for Numark Mixtrack Pro FX

[Qwertie-]

Bug Description

With the default configuration/mapping, the FX select buttons have unexpected mappings.
For example, currently in Mixxx, pressing "Echo" scrolls/selects the effects on deck one, while pressing phaser scrolls the effects on deck two. Pressing reverb adjusts the beat grid.

My expectation is that pressing an effect button like Echo would set the effect on both decks to echo. Which is it what it does in VirtualDJ and Serato. I can see how possibly mapping them to other functions could be useful, but I'd think that having the default mapping match what's printed on the buttons would make most sense.

I'm happy to try to put up a PR to change the mapping, just wanted to discuss first.

Version

2.4.1

OS

MacOS

[ronso0]

I agree the fx mapping is not intuitive.
The mapping is documented here https://manual.mixxx.org/2.4/en/hardware/controllers/numark_mixtrack_pro_fx
(that link is also in the mapping info box in the preferences)

FYI Mixxx has evolved since this mapping has last been edited. There are now dedicated effect load controls and the mapping can make use of them. IIRC this something like this has been implemented for the Traktor S3
#11199