Initial Frontend

Still TODO:

• Can't reach backend notification
• Implement SyncSaber
• Display progress
• Test PlaylistUpdate event
• Improve UX
  • Don't flash UI
  • Disable some buttons while progressing
    • Install core mods button
    • Installing/Uninstalling mods
• Add virtual scroller in Songs view (otherwise it takes a long time to load)
• Add import via file upload

Moved to issues #21 (closed) #20 #19 (closed) #18 #17 (closed) #16 (closed)