Excluded miles in Trip Fee per mile calculation

Add in an excluded miles field for service areas so that we can set a certain amount of miles included before charging trip fees on a per mileage fee.

For example, we don't charge trip fees for up to a 30 mile radius of our office, anything over 30 miles we want to charge a trip fee of $1.5 per mile.

Currently we need to use the default tiered model and build out each mile and its corresponding fee.

With this change we could exclude the 30 miles and easily setup trip fees on a per mileage basis.