Refactor invitation creation
clicking subscribe/unsubscribe will send an ajax request, then update the list view accordingly
change styling on subscribe/unsubscribe buttons
fix errors in the grocery lists controller
fix bug where debts wouldnt be assigned when creating an expense from a list on the dashboard
fix bug where if a user is the only subscriber and buys a list, it would create two debts
Merge branch 'master' into dashboard-subscribe-list