uploads: use storage manager to distribute files.

Refactors the upload process to pass around temp files, rather than
passing around file paths and directly writing output to the local
filesystem. This way we can pass the storage manager the preview /
sample / original temp files, so it can deal with storage itself.

* Change Download::File#download! to return a temp file.

* Change DanbooruImageResizer and PixivUgoiraConverter to accept/return
  temp files instead of file paths.

* Change Upload#generate_resizes to return temp files for previews and samples.

* Change Upload#generate_resizes to generate ugoira .webm samples
  synchronously instead of asynchronously.

app/logical/pixiv_ugoira_converter.rb

@@ -1,13 +1,9 @@
 class PixivUgoiraConverter
-  def self.convert(source_path, output_path, preview_path, frame_data)
-    folder = Zip::File.new(source_path)
-    write_webm(folder, output_path, frame_data)
-    write_preview(folder, preview_path)
-    RemoteFileManager.new(output_path).distribute
-    RemoteFileManager.new(preview_path).distribute
-  end
+  def self.generate_webm(ugoira_file, frame_data)
+    folder = Zip::File.new(ugoira_file.path)
+    output_file = Tempfile.new(binmode: true)
+    write_path = output_file.path
 
-  def self.write_webm(folder, write_path, frame_data)
     Dir.mktmpdir do |tmpdir|
       FileUtils.mkdir_p("#{tmpdir}/images")
       folder.each_with_index do |file, i|
@@ -64,14 +60,17 @@ class PixivUgoiraConverter
         return
       end
     end
+
+    output_file
   end
 
-  def self.write_preview(folder, path)
-    Dir.mktmpdir do |tmpdir|
-      file = folder.first
-      temp_path = File.join(tmpdir, file.name)
-      file.extract(temp_path)
-      DanbooruImageResizer.resize(temp_path, path, Danbooru.config.small_image_width, Danbooru.config.small_image_width, 85)
-    end
+  def self.generate_preview(ugoira_file)
+    file = Tempfile.new(binmode: true)
+    zipfile = Zip::File.new(ugoira_file.path)
+    zipfile.entries.first.extract(file.path) { true } #  'true' means overwrite the existing tempfile.
+
+    DanbooruImageResizer.resize(file, Danbooru.config.small_image_width, Danbooru.config.small_image_width, 85)
+  ensure
+    file.close!
   end
 end