Add default site customization pages

From now on these static pages:

`/privacy'
`/conditions'
`/accesibility'
`/help/faq'
`/welcome'

have been moved to the DB and can be modified easily by any
administrator in `/admin/site_customization/pages'

spec/lib/tasks/db_spec.rb

@@ -0,0 +1,15 @@
+require "rails_helper"
+
+describe "rake db:pages" do
+  let :run_rake_task do
+    Rake.application.invoke_task("db:pages")
+  end
+
+  it "seeds the database with the default custom pages" do
+    SiteCustomization::Page.destroy_all
+    expect(SiteCustomization::Page.count).to be 0
+
+    run_rake_task
+    expect(SiteCustomization::Page.count).to be 7
+  end
+end