RacksDB assets

All assets are generated based on the content of branding.svg and screenshots/raw/ by running this command:

$ ./update-assets

This automatically generates:

Scalable SVG files of the logo in scalables/ folder,
Bitmaps PNG files (in various sizes) of the logo in bitmaps/ folder,
Favicon in bitmaps/ folder,
Shadowed and Webp compressed versions of raw PNG screenshots.

The script has some requirements:

Python3
Ninja build system. On Debian/Ubuntu, this can be installed with:
```
$ sudo apt install ninja-build
```
Inkscape
RFL build package
Scour Python package
ImageMagick

All the generated files are commited and pushed in Git repository to allow direct usage by documentation site, main README.md file, etc…