Enrich the mirror image base

[freshsomebody]

According to the Move Mirror blogpost, they used 80,000 mirror images for matching. As you can see, the image base of this project is currently way less than enough.

If you're interested in enriching the image base, feel free to make PR to add/update/delete images at assets/images/mirror-poses.

Followings are the recommended procedures:

1. Add images into assets/images/debug
2. Use http://localhost:3000/debug/matching to check whether there were very similar images already
3. Add images into assets/images/mirror-poses
4. Use http://localhost:3000/debug/mirrorImages to check the image qualities
5. Remove those images with bad qualities
6. Use http://localhost:3000/debug/mirrorImages to rebuild vp tree

To ensure the best matching quality and user experience, updated images are better to fit with requirements below:

1. Full-body poses are better
2. The pose parts should be accurate enough
3. The size of an image is better not bigger than 50kb
4. The image names are better to be semantic
5. Images from all kinds of sources (yourself, Internet, etc.) are all welcome, but please watch out the content appropriateness and respect the copyright if there are

Thank you for being interested in this project and wanting to fulfill it. Hope you can find some joy from it!