Remap the EQ and mixer FX for decks C&D to the stem volume controls for decks A&B

Can be disabled/enabled using SHIFT+STEMS.

Press SHIFT+FILTER button on the corresponding side to set that set of EQs + filter (deck C/D) to act as stem filter controls and enable stem filters. Press shift+filter again to disable this change, and the filters themselves.

Also made the FX arrow indicators for decks C&D display the status of the mod: to one side mod enabled, to the other, filters also enabled. Seemed like the best place to display if you're not using those decks anyway (and unfortunately the filter light gets overridden if you change channel FX, so couldn't really use that).