Plugin Toggle & Slider Listener

This would allow plugins to get toggle(without a workaround) and slider values from the client.

It has always been suggested that at some point there would have to be a UI rework when it comes to plugins to allow for more capabilities and possibly the ability to use Sleek. I feel like adding methods only to remove them soon™ would be counter intuitive. However, with this being said, it still might be good to just release those methods in the meantime anyways as the current situation really does limit us way too much.