Make use of manifest aliases when generate SVG symlinks

[grische]

Currently in a target file there are aliases defined. As the aliases should always have the same image, we would like to auto-generate symlinks for all aliases.

For example: https://github.com/freifunk-gluon/gluon/blob/73fce2e960a722d96c330711be9eb645ed501edb/targets/bcm27xx-bcm2710#L5

We can either use a manually-curated list of aliases or automatically parse gluon (during runtime) and generate the alias symlinks on the fly.