Slight improvements to event registration

NAgoya BOOK CENTER's events have all been impressive, and that has driven an increase in site traffic. I'm very grateful. The other day someone asked if we could add a "歌会" category, and after I set it up an event was already registered. Fast! I occasionally review the structure of the event pages, and I adjusted things because the sign-up button can be hard to see on smartphones. Also, since I heard that people couldn't find where to cancel, I decided to include that information in the registration confirmation email. Ideally it would be nice to show a list on the user's settings page, but I'll consider that if sign-ups increase.