Set member status to sustainer upon payment

Introduces a state machine for the payment status as well.

refs #213

app/controllers/contributions/donations_controller.rb

@@ -11,7 +11,7 @@ class Contributions::DonationsController < ApplicationController
   def index
     @current_section = :contributions
     @donations_completed = current_user.donations.completed.order('paid_at desc')
-    @donations_pending = current_user.donations.processing.order('created_at desc')
+    @donations_processing = current_user.donations.processing.order('created_at desc')
 
     if Setting.lndhub_enabled?
       begin
@@ -81,14 +81,11 @@ class Contributions::DonationsController < ApplicationController
 
     case invoice["status"]
     when "Settled"
-      @donation.paid_at = DateTime.now
-      @donation.payment_status = "settled"
-      @donation.save!
+      @donation.complete!
       flash_message = { success: "Thank you!" }
     when "Processing"
       unless @donation.processing?
-        @donation.payment_status = "processing"
-        @donation.save!
+        @donation.start_processing!
         flash_message = { success: "Thank you! We will send you an email when the payment is confirmed." }
         BtcpayCheckDonationJob.set(wait: 20.seconds).perform_later(@donation)
       end