Simplify icons sprite build

By integrating each image in base64 in a single SVG file, the build could be simplified and somes dependencies removed.

See an example of what I would like to implement : https://up.nicofrand.eu/test_svg/

We would need to be able to:

• know the dimensions of an image (if the dimensions differ, else we can just hardcode it in the script)
• transform the image in base64