feat(pepicons.com): Favourite icons

[mesqueeb]

UI

• heart icon to left of icon modal
• same color as bottom section
• same size as the code buttons
• should always use type="pencil"
• "favourited" should show heart-filled instead, and have the "main" color that the user picked

Behaviour

• when you click to favourite an icon, it should save it to localStorage
• IF the local storage is empty and no icons have been saved yet
  • the modal should close and the website should smooth scroll to the top
  • there as a first new category we see Favourites and there the icon you just favourited is seen
• IF we already have 1 or more icons favourited, then we just make the heart icon the main color without closing the modal

be sure the favourited icons are persisted on page refresh