Improve themeing support

[leetftw]

• Allow for animations
  • Maybe add an option for timers?
  • How would we present this in a config file?
  • Maybe multiple timers at different intervals for different concurrent animation speeds?
• Add stretch option for each resource usable in ImageRenderer
• Improve Luna's screenshots Add XP visual style renderer
• Implement Quick Launch rendering
• Add layout options (constraints, padding, margin etc.)
• Preview theme in the config menu

[Craftplacer]

I would suggest adding layout metrics too (padding, margin, sizes, size constraints, etc.) for more flexible designs.