Admin improvements
Merge branch 'master' of github.com:upptalk/uppsell
Merge pull request #9 from xesco/master

Added payment_state, order_state and username to invoice model + migration
Invoice admin bug
Fix merge conflicts
Merge branch 'master' of github.com:upptalk/uppsell
Added export to CSV capability to Invoices
Merge branch 'master' of https://github.com/upptalk/uppsell