Switch to SVG icons #119

Note: While developing we can choose to keep Bootstrap Icons for now, makes it easy to switch

Punting to 0.2 since SVG implementation is done and for development we'll keep using the Bootstrap icon library just for simplicity.
Of course we could switch in the meantime but it's no priority.

Might be nice to look into this as well: https://ux.symfony.com/icons
Perhaps it could fully replace our custom icon handler and allow modules to include other icons as well.