move presets documentation to Module Reference

[deekayhd]

The documentation for managing presets is currently at content/darkroom/processing-modules/presets.md. The documentation mentions that parts of it are also valid for utility modules. Therefore, I propose to move the page to content/module-reference/. Unfortunately, I cannot provide a PR directly, because I do not know how to define the position in the hierarchy. I assume it is by just moving the file, but I do not know how to test it.