RB 5/6 + DDJ - Improve the mapping abilities for parameters buttons

With the DDJ RX on RB 5/6, we're unable to map / remap the parameters buttons for certain pads mode.

- On RB's side, these two buttons do not appear for certain pads modes in the midi tool. Therefore they can't be selected.

- On RB's side, apparently there's no way to map the scroll under hotcues and pad FX modes for example.

- On the DDJ RX, parameters buttons looks inactive in hotcues mode. That would be great if it could jump to cue 9 to 16.

- On the DDJ RX, parameters buttons in pad FX mode are made to change the time length of an FX. But shift + these buttons would be nice to access to the second layer of FX's (available on screen with the scroll)

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