[Feature Request] Resize image grid based on window size.

[nikolaizombie1]

Currently waypaper reads from the config file to know how many columns to make on the image grid. However, it would be much more elegant if the amount of columns change based on the window size. This would allow waypaper to feel more responsive in larger displays and to utilize the screen real estate more effectively.

[anufrievroman]

It would certainly be better, but I couldn't get the app dimensions in GTK to adjust the number of columns. If someone wants to try, please :)