Comment 1 for bug 1896832

IIRC the this was supposed to avoids situations after start that are kinda hard to debug. If the orientation switches have been changed unnoticed previously, or 'in the heat of the night'.
Now (2.3) all skins (except Shade) show the crossafder switches both in 2- and 4-deck mode. Only in Tango skin they are in an unusual position, not the mixer, which is also far from the mixer.

There are at least two use cases that are affected by crossfader/orientation persistence. I assume they affect the 4-decks mode only, so we can ignore Shade skin here.

1. multiple DJs share a computer during a set and want to switch between regular crossfader usage and 'all channels centered, crossfader ignored' without the need to flip all decks switches and show/hide the crossfader via Skin Settings.

 For that we could add an option to Preferences > Crossfader called
 "Ignore crossfader", plus a CO that can be mapped in skins and on
 controllers.
 Toggle "Ignore crossfader" ON does
 * (center the crossfader, store position??)
 * store orientation of all decks
 * put all decks into their default position
 * hide the crossfader in skins
 * ignore crossfader input from controllers
 Toggle OFF does
 * restore orientation of all decks
 * (restore crossfader position??)
 * show the crossfader in skins

2. Save & restore the custom channel orientation across restarts
Example: outer decks 3/4 are left/right, decks 1+2 are always centered.
 It's tempting to add a respective option into the Decks preferences page
 (default off). But actually, since it's tightly coupled to the crossfader
 and the deck page is crammed already, it should better be in the
 Crossfader page.