Expose generic functionality / function library

[husberg-disguise]

Issue #35 has repeatedly come up, but would require RenderStream API changes that would generally not be beneficial to the platform.

Instead, collate the most used functionality and expose it as a collection of fields that can be easily enabled in the plugin settings without having to modify exposed variables in the blueprint of each level.

Examples would be:

• Performance tooling: engine scalability slider, stat overlays and starting/stopping of profiling to disk
• Camera post-effects/screen-space effects that may or may not work for split viewports
• Anything the community can think of, so ideally easily extensible