feat: Pioneer DDJ-REV1 mappings

[LauraRozier]

Controller mappings for the Pioneer DDJ-REV1

Skipped features (don't exist within Mixxx):

• TrackingScratch Mode Pads
• Trans Mode Pads
• ScratchBank Mode Pads

Still a draft while I test things and work out some quirks / docs

[JoergAtGithub]

Welcome at Mixxx!
As a first-time contributor we need you to sign the Mixxx Contributor Agreement and comment here when you have done so. It gives us permission to distribute your contribution under the GPL v2 or later license and the Apple Mac App Store. It is also helpful for us to have contact information for contributors in case we may need it in the future.

[JoergAtGithub]

The pre-commit check is failing. The best way to fix pre-commit issues is to install pre-commit locally on your system, as described here: https://github.com/mixxxdj/mixxx/wiki/Using-Git#set-up-automatic-code-checking
Than it will fix these issues automatically before every commit.
Alternatively, you can download the pre-commit.patch file from the artifacts of this PR

unzip it, and apply it using:
git apply pre-commit.patch

[LauraRozier]

Yep, that's why it's in DRAFT mode. ^_^ Work in progress, so builds will fail.
Did the 'ol contributor agreement thing just now as well.

As for documenting the whole shebang for the manual.. That might take some time.. ^_^"
I'm fast with things I enjoy working on, but hella slow with docs.

Currently I'm experiencing some troubles getting the FX buttons to light up properly, this looks like an issue with the controller itself, rather than Mixxx's mapping. When pressing the FX button it lights up, then immediately goes off again, even though the effect stays on in Mixxx, from that point forwards the button acts inverted. It's weird..
I'm talking about buttons 3,4,5 in the image below

EDIT: They do work correctly when toggled within Mixxx itself. They only miss-behave when using them on the controller itself. If anyone has any ideas, feel free to suggest. ^_^