Added gruvbox theme

assets/images/amoled.png

assets/images/amoled@220.png

assets/images/amoled@266.png

assets/images/amoled@335.png

assets/images/amoled@352.png

assets/images/amoled@532.png

assets/images/amoled@thumb.jpg

assets/images/generate_assets.sh

assets/images/gruvbox_dark.png

assets/images/gruvbox_dark@220.png

assets/images/gruvbox_dark@266.png

assets/images/gruvbox_dark@335.png

assets/images/gruvbox_dark@352.png

assets/images/gruvbox_dark@532.png

assets/images/gruvbox_dark@thumb.jpg

assets/images/gruvbox_light.png

assets/images/gruvbox_light@220.png

assets/images/gruvbox_light@266.png

assets/images/gruvbox_light@335.png

assets/images/gruvbox_light@352.png