Add the possibility to allow the user to have a favicon which differs from the main...

Add the possibility to allow the user to have a favicon which differs from the main logo (#18542)

* Changed the filename of the favicon SVG

This allows the user to have a favicon which differs from the logo.

* Added favicon.svg

This is needed to accommodate the changes for allowing the user to have a differing logo and favicon

* Adjusted page to accommodate what icon is used as favicon

* Added functionality to also generate the favicon.svg via generate-images.js

* Adjusted the description for the new favicon compatibility

Co-authored-by: silverwind <me@silverwind.io>
* Updated generate-images.js to generate favicons from a separate favicons.svg file

This belongs to PR #18542.

* Added description on how custom favicons can be generated

* Replaced space indents with tabs

* Synced changes with current state of the file

* Synced changes with current state of the file

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Lauris BH <lauris@nix.lv>