Implement Weekly Schedules & Tracklists

[BGMP]

This PR introduces the long-awaited feature to generate RVA's weekly schedules on-site! This is rather a minimal implementation of the feature, but for our purposes I think it will work nicely.

Details:

• This new section allows organizers and admins to generate track lists for every day of week, following RVA's format: 20 tracks are picked randomly for every 2 days. First day's tracklist are the normal version of the picked tracks, and second day's assigned the R version of those tracks.
• The listing of track lists on-site also allows organizers to download each individual track list as PNG images.

Observations:

• Future work is required to only allow the selection of Mondays as the "start_date" of a weekly schedule.

[nickskyline]

LGTM. The updated styles make the downloadable images look way better in discord. "Play" section could be a good place to add the hyperlink of the schedules.

[BGMP]

LGTM. The updated styles make the downloadable images look way better in discord. "Play" section could be a good place to add the hyperlink of the schedules.

Good idea. I'll ship this initial implementation and then edit the "Play" section!