added pdf/print for pos
added some defaults and links to views
updated api to expose po and po-li attributes
updated api - fixed attribute bugs
html clean up and adjustments
removed arrival from po model - fixes #42
added optional tracking url to po model -- closes #43
changed po pdf layout -- closes #38
added li attributes to po pdf -- closes #39
perform cost adjustment from po form -- fixes #37
added shipping cost to po model -- fixes #40
added login_required decorator in views