Add id to ticket purchase form.

This disambiguates it from other forms that might appear on the same
page. (Namely, the waiting list form, which will come in a few commits.)
Add soft and hard limits for ticket purchases.

At the hard limit, the controller starts to reject ticket purchases. At
the soft limit, the view stops displaysing available tickets. This is
friendlier for the user, since it's unlikely they'll try purchasing
tickets, then have the model reject them later on.
Add ticket waiting list (- model).

This commit adds the ticket waiting list route, controller action, and
view. The model was generated previously, in commit
dvdhsu/hughsball@386093666f4e75ea6c2443e9bdf8a8ca42f204f1.
Remove extra whitespace in routes file.