New Group Discount function

When you create a trip or edit a trip in the Price page you can now vary how your group discounts are calculated.
Choose Discount per person
"Amount" is amount discount per person for the group
Start with first discount group size
i.e. once I have 4 people take $10 off each
Once I have 8 take $20 off each.
In this sample 4-7 people will have $10 off , over 8 will get $20 off