CatEventUsers update to discounts on the show page

- Now discounts carry through from an admin creating one, to a user
  going to a page seeing they have said discount that admin created and
  then clicking purchase the amount carries through using discount tier
  calculation.

Bug that I noticed:
- Discounts are not working for a user if the user logs in with Google.
  An admin can set said discount but for some reason the app is not
  recognizing the discount when the user logs in.  Even though we are
  looking it up via
  CatEventUser.find_by_user_id(current_user.id).discount(tier)

Explore this further.