Always show event attendance form
Closes #232 (closed).
The event attendance form is now always shown on an event, making it more convenient to change your registered attendance.
Additional changes:
- Now shows a message when you create/update an attendance. This was primarily done because there was a lack of feedback after you had created/updated your attendance when the form didn't disappear.
- Added horizontal rule between event description and attendance form. I felt like a stronger separation was nice.