Use natsort.os_sorted to sort files in the browser

[wkentaro]

Close #955
Close #989
Close #953

It seems there're many needs for sorting files naturally in the file browser.
With a bit of research, I have decided to use natsort.os_sorted, since it is at least to me the most "natural" if files are sorted as the same way as the file manager of an OS (I use Finder on macOS).

Below is an example of the result:

import re
import natsort

filenames = [
    "img_1.jpg",
    "img_100.jpg",
    "img_10.jpg",
    "img_11.jpg",
    "img_1-1.jpg",
    "img_12-1.jpg",
]

print("original  :", filenames)
print(
    "re.sub(\D):",
    sorted(filenames, key=lambda x: int(re.sub("\D", "", x.lower()))),
)
print("natsorted :", natsort.natsorted(filenames))
print("os_sorted :", natsort.os_sorted(filenames))

print()

filenames = [
    "image1.png",
    "image10.png",
    "image2.png",
    "image200.png",
    "image3.png",
]
print("original  :", filenames)
print(
    "re.sub(\D):",
    sorted(filenames, key=lambda x: int(re.sub("\D", "", x.lower()))),
)
print("natsorted :", natsort.natsorted(filenames))
print("os_sorted :", natsort.os_sorted(filenames))

original  : ['img_1.jpg', 'img_100.jpg', 'img_10.jpg', 'img_11.jpg', 'img_1-1.jpg', 'img_12-1.jpg']
re.sub(\D): ['img_1.jpg', 'img_10.jpg', 'img_11.jpg', 'img_1-1.jpg', 'img_100.jpg', 'img_12-1.jpg']
natsorted : ['img_1-1.jpg', 'img_1.jpg', 'img_10.jpg', 'img_11.jpg', 'img_12-1.jpg', 'img_100.jpg']
os_sorted : ['img_1.jpg', 'img_1-1.jpg', 'img_10.jpg', 'img_11.jpg', 'img_12-1.jpg', 'img_100.jpg']

original  : ['image1.png', 'image10.png', 'image2.png', 'image200.png', 'image3.png']
re.sub(\D): ['image1.png', 'image2.png', 'image3.png', 'image10.png', 'image200.png']
natsorted : ['image1.png', 'image2.png', 'image3.png', 'image10.png', 'image200.png']
os_sorted : ['image1.png', 'image2.png', 'image3.png', 'image10.png', 'image200.png']