Add `Term` model to keep track of terms

app/models/application_setting/term.rb

+class ApplicationSetting
+  class Term < ActiveRecord::Base
+    validates :terms, presence: true
+  end
+end

app/views/admin/application_settings/_terms.html.haml

+= form_for @application_setting, url: admin_application_settings_path, html: { class: 'form-horizontal fieldset-form' } do |f|
+  = form_errors(@application_setting)
+
+  %fieldset
+    .form-group
+      .col-sm-12
+        .checkbox
+          = f.label :enforce_terms do
+            = f.check_box :enforce_terms
+            = _("Require all users to accept Terms of Service when they access GitLab.")
+          .help-block
+            When enabled, users cannot use GitLab until the terms have been accepted.
+    .form-group
+      .col-sm-12
+        = f.label :terms do
+          = _("Terms of Service Agreement")
+      .col-sm-12
+        = f.text_area :terms, class: 'form-control', rows: 8
+        .help-block
+          Markdown enabled
+
+  = f.submit 'Save changes', class: "btn btn-success"

db/migrate/20180424134533_create_application_setting_terms.rb

+class CreateApplicationSettingTerms < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def change
+    create_table :application_setting_terms do |t|
+      t.integer :cached_markdown_version
+      t.text :terms, null: false
+      t.text :terms_html
+    end
+  end
+end

db/schema.rb

@@ -40,6 +40,12 @@ ActiveRecord::Schema.define(version: 20180503150427) do
     t.text "new_project_guidelines_html"
   end
 
+  create_table "application_setting_terms", force: :cascade do |t|
+    t.integer "cached_markdown_version"
+    t.text "terms", null: false
+    t.text "terms_html"
+  end
+
   create_table "application_settings", force: :cascade do |t|
     t.integer "default_projects_limit"
     t.boolean "signup_enabled"