Handle Stripe invoice.payment_succeeded webhook event

[joshsmith]

Problem

• We should handle the invoice.payment_succeeded event
• We store the invoice in a local table

field :amount_due
field :application_fee

field :id_from_stripe
field :charge_id_from_stripe
field :customer_id_from_stripe
field :subscription_id_from_stripe

belongs_to :user # can figure it out through customer
belongs_to :subscription

# any other fields that make sense

• we then track the event. tracking should contain a user id

[begedin]

@joshsmith Updated the issue with information from our Slack conversation