text: Title: [Feature Request] dcc.Slider - Enable user to define slider direction
  Body: 
  I have an application where I am like to use sliders to crop an image (heatmap graph). The image's (0,0) is defined as the top left of the image. I'd like the y slider to start with 0 at the top, and end with the height of the image at the bottom. Currently, I cannot find a method to invert the slider to allow for the slider to go {top: low, bottom: high}, instead of the default {top: high, bottom: low} 
  
  
  
  **Describe the solution you'd like**
  A slider where the direction from minimum to maximum could be swapped. 
  
  **Describe alternatives you've considered**
  I tried setting the min to be higher than the max, did not work.
  I've tried flipping the slider with CSS and the result is... erratic
  
  
  