Zweischneidige kalender

[bl00dymarie]

Adding the swiss-army-knife calendar, incl. 1 migration:

• 3 different views HoC, other & all events
• Adding show_all_events to calendars for easy way to show all events
• Adding buttons for the inactive calendars to allow smooth switching (yeah)
• Seeding accordingly, nicer image for blogpost

Closes #56 \o/

[bl00dymarie]

Thank you @berlintam for your awesome review!