ci: add python script for batch svg to .ico conversion

[Cyklon3000]

This script allows for batch conversion of the .svg's in the svg folder, making it quicker to use the icons.
This script allows for multiple .svg's to be combined in a single .ico file, as requested in #11.

By default the .ico sizes 16, 32, 48, 64, 256 are created, because windows only respects these intervals for folders.
The conversion takes place in a subprocess using ImageMagick with the magick console command. For the script to work therefore, an installation of ImageMagick to the path is required. This is still easier and quicker than previous solutions.

The combination of multiple .svg's into a single .ico file is orchestrated under a new naming convention that appends the maximum size until which the base .svg is replaced in the .ico file with the smaller versions of the variant.
This way variants remain optional, but are made possible without adjustment in regular operation.
folder_icon-48px.svg overwrites folder_icon.svg for the sizes until and including 48px. After that the .ico is filled with with scaled versions of folder_icon.svg or other variants, for example a potential folder_icon-64px.svg

[Cyklon3000]

This pr is rather a response to #11 with the mentioned complications to batch conversion than a serious addition to the repository. Rather the workflow, but I did not find the place to commit regarding this,