Add shipping carrier service info

[dsposito]

Add a service property to the Package class for storing the shipping service (Ground, Priority, Express, etc).

UPS: http://www.reddit.com/r/LifeProTips/comments/1r81rp/lpt_the_first_six_digits_of_a_ups_tracking_number/

USPS: Services: https://tools.usps.com/go/TrackConfirmAction_input