Rethink folder structure

[Botffy]

Currently mostly everything is just in the src root (except totally reusable components like TimeAgo).

@egkrly proposed a feature based system, and we do have multiple independent features:

• stat pages (Bikes.vue, TimePage.vue etc, whose name could be standardised to *StatPage.vue)
• adding rides (RideForm.vue, RideFormByScreenshot.vue, the celebration service)
• the mostly static pages like InfoPage

ride-service.ts doesn't really play nice with this, especially since it reads and writes firestore data and also calculates celebrations (which it shouldn't). But it can be split into a "read rides from firestore" and "write ride to firestore" service.