Add option for FOSS contribution payments (#730)

* First commit

* Use subscription flow for monetary contributions

* Removed only part of the SPAN

* Localize Stripe payments message

* More localization of contribution strings

* Missed two billing to payment changes

* Fix tests

* Localization of "Open Demo" strings

* Fix grammar error

* Update for consistency

* Localize CTA

* More localilzation strings

app/controllers/subscriptions_controller.rb

@@ -5,7 +5,7 @@ class SubscriptionsController < ApplicationController
   # Upgrade page for unsubscribed users
   def upgrade
     if Current.family.subscription&.active?
-      redirect_to root_path, notice: "You are already subscribed."
+      redirect_to root_path, notice: "You are already contributing. Thank you!"
     else
       @plan = params[:plan] || "annual"
       render layout: "onboardings"