Allow user to disable the boost confirm dialog in preferences

config/locales/simple_form.en.yml

@@ -29,6 +29,7 @@ en:
         setting_default_privacy: Post privacy
         type: Import type
         username: Username
+        setting_boost_modal: Show confirmation dialog before boosting
       interactions:
         must_be_follower: Block notifications from non-followers
         must_be_following: Block notifications from people you don't follow

config/settings.yml

@@ -7,6 +7,7 @@ defaults: &defaults
   site_contact_email: ''
   open_registrations: true
   closed_registrations_message: ''
+  boost_modal: true
   notification_emails:
     follow: false
     reblog: false