Enable registration to proceed without requiring a ticket.

Requiring a ticket after registration is convoluted; while it may be neccesary
for some workflows, it definitely isn't for others, and the core of osem
doesn't need it... so let's make it optional.

app/models/admin_ability.rb

@@ -117,10 +117,7 @@ class AdminAbility
     can :manage, Commercial, commercialable_type: 'Conference',
                              commercialable_id:   conf_ids
     can :manage, Registration, conference_id: conf_ids
-    can :manage, RegistrationPeriod do |registration_period|
-      conference = registration_period.conference
-      conf_ids.include?(conference.id) && conference.tickets.for_registration.any?
-    end
+    can :manage, RegistrationPeriod, conference_id: conf_ids
     can :manage, Booth, conference_id: conf_ids
     can :manage, Question, conference_id: conf_ids
     can :manage, Question do |question|

app/models/conference.rb

@@ -29,11 +29,7 @@ class Conference < ApplicationRecord
   has_many :ticket_purchases, dependent: :destroy
   has_many :payments, dependent: :destroy
   has_many :supporters, through: :ticket_purchases, source: :user
-  has_many :tickets, dependent: :destroy do
-    def for_registration
-      where(registration_ticket: true)
-    end
-  end
+  has_many :tickets, dependent: :destroy
   has_many :resources, dependent: :destroy
   has_many :booths, dependent: :destroy
   has_many :confirmed_booths, -> { where(state: 'confirmed') }, class_name: 'Booth'

app/models/ticket.rb

@@ -10,6 +10,8 @@ class Ticket < ApplicationRecord
 
   monetize :price_cents, with_model_currency: :price_currency
 
+  scope :for_registration, -> { where(registration_ticket: true) }
+
   # This validation is for the sake of simplicity.
   # If we would allow different currencies per conference we also have to handle convertions between currencies!
   validate :tickets_of_conference_have_same_currency