Uploads for admin site settings (#4913)

* Improve OpenGraph tags for about pages

* Add thumbnail admin setting

* Fix error

* Fix up

app/models/site_upload.rb

@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+# == Schema Information
+#
+# Table name: site_uploads
+#
+#  id                :integer          not null, primary key
+#  var               :string           default(""), not null
+#  file_file_name    :string
+#  file_content_type :string
+#  file_file_size    :integer
+#  file_updated_at   :datetime
+#  meta              :json
+#  created_at        :datetime         not null
+#  updated_at        :datetime         not null
+#
+
+class SiteUpload < ApplicationRecord
+  has_attached_file :file
+
+  validates_attachment_content_type :file, content_type: /\Aimage\/.*\z/
+  validates :var, presence: true, uniqueness: true
+
+  before_save :set_meta
+  after_commit :clear_cache
+
+  def cache_key
+    "site_uploads/#{var}"
+  end
+
+  private
+
+  def set_meta
+    tempfile = file.queued_for_write[:original]
+
+    return if tempfile.nil?
+
+    geometry  = Paperclip::Geometry.from_file(tempfile)
+    self.meta = { width: geometry.width.to_i, height: geometry.height.to_i }
+  end
+
+  def clear_cache
+    Rails.cache.delete(cache_key)
+  end
+end