Use default_url_options to generate absolute URLs

In the dev seeds, we were using `Setting["url"]/proposals`, but we can
use `proposals_url` instead, similar to what we do in the rest of the
application.

We can do a similar thing in the sitemap. This way the sitemap will also
work on installations who haven't manually set the "url" setting.

Since we aren't using `Setting["url"]` anywhere anymore, we're removing
it.

This setting was mainly redundant, since we already had the
`server_name` in the secrets. Furthermore, `server_name` is
automatically configured when running the installer, while
`Setting["url"]` had to be manually set in the admin section the
application was installed.

Note we're using `ActionMailer::Base` setting to generate URLs. Sounds a
bit strange, but it's a standard way Rails provides to generate URLs
outside the context of a request.

app/models/setting.rb

@@ -159,7 +159,6 @@ class Setting < ApplicationRecord
         "twitter_handle": nil,
         "twitter_hashtag": nil,
         "youtube_handle": nil,
-        "url": "http://example.com", # Public-facing URL of the app.
         # CONSUL installation's organization name
         "org_name": "CONSUL",
         "meta_title": nil,

config/locales/en/settings.yml

@@ -40,8 +40,6 @@ en:
     telegram_handle_description: "If filled in it will appear in the footer"
     instagram_handle: "Instagram handle"
     instagram_handle_description: "If filled in it will appear in the footer"
-    url: "Main URL"
-    url_description: "Main URL of your website"
     org_name: "Site name"
     org_name_description: "This name will appear on mailers subject, help pages..."
     related_content_score_threshold: "Related content score threshold"

config/locales/es/settings.yml

@@ -40,8 +40,6 @@ es:
     telegram_handle_description: "Si está rellenado aparecerá en el pie de página"
     instagram_handle: "Usuario de Instagram"
     instagram_handle_description: "Si está rellenado aparecerá en el pie de página"
-    url: "URL general de la web"
-    url_description: "URL principal de tu web"
     org_name: "Nombre del sitio"
     org_name_description: "Este nombre aparecerá en el asunto de emails, páginas de ayuda..."
     related_content_score_threshold: "Umbral de puntuación de contenido relacionado"

config/sitemap.rb

@@ -9,7 +9,7 @@ SitemapGenerator::Sitemap.namer = SitemapGenerator::SimpleNamer.new(:sitemap, ex
 
 # default host
 SitemapGenerator::Sitemap.verbose = false if Rails.env.test?
-SitemapGenerator::Sitemap.default_host = Setting["url"]
+SitemapGenerator::Sitemap.default_host = root_url(ActionMailer::Base.default_url_options)
 
 # sitemap generator
 SitemapGenerator::Sitemap.create do

db/dev_seeds/admin_notifications.rb

@@ -4,7 +4,10 @@ section "Creating Admin Notifications & Templates" do
       %i[title body].index_with do |attribute|
         -> { I18n.t("seeds.admin_notifications.proposal.#{attribute}") }
       end
-    ).merge(link: "#{Setting["url"]}/proposals", segment_recipient: "administrators")
+    ).merge(
+      link: Rails.application.routes.url_helpers.proposals_url(ActionMailer::Base.default_url_options),
+      segment_recipient: "administrators"
+    )
   ).deliver
 
   AdminNotification.create!(

db/dev_seeds/settings.rb

@@ -18,7 +18,6 @@ section "Creating Settings" do
     "telegram_handle": "CONSUL",
     "twitter_handle": "@consul_dev",
     "twitter_hashtag": "#consul_dev",
-    "url": "http://localhost:3000",
     "votes_for_proposal_success": "100",
     "youtube_handle": "CONSUL"
   }.each do |name, value|