Add ability to set hCaptcha either on registration form or on e-mail validation

Upshot of CAPTCHA on e-mail validation is it does not need to break the in-band
registration API.

app/views/admin/settings/edit.html.haml

@@ -45,7 +45,7 @@
 
   - if captcha_available?
     .fields-group
-      = f.input :captcha_enabled, as: :boolean, wrapper: :with_label, label: t('admin.settings.captcha_enabled.title'), hint: t('admin.settings.captcha_enabled.desc_html')
+      = f.input :captcha_mode, as: :radio_buttons, collection: %w(disabled registration-form email-confirmation), include_blank: false, wrapper: :with_block_label, label_method: ->(type) { safe_join([t("admin.settings.captcha.#{type}.title"), content_tag(:span, t("admin.settings.captcha.#{type}.desc_html"), class: 'hint')])}, label: t('admin.settings.captcha.title'), hint: t('admin.settings.captcha.desc_html')
 
   %hr.spacer/
 

app/views/auth/confirmations/captcha.html.haml

@@ -0,0 +1,11 @@
+- content_for :page_title do
+  = t('auth.confirm_captcha')
+
+= form_tag auth_captcha_confirmation_url, method: 'POST', class: 'simple_form' do
+  = hidden_field_tag :confirmation_token, params[:confirmation_token]
+
+  .field-group
+    = render_captcha_if_needed
+
+  .actions
+    %button.button= t('challenge.continue')