uploads: factor out image dimension and filetype detection code.

* Add MediaFile abstraction. A MediaFile represents an image or video file.
* Move filetype detection and dimension parsing code from uploads to MediaFile.

app/logical/media_file/flash.rb

@@ -0,0 +1,6 @@
+class MediaFile::Flash < MediaFile::Image
+  def dimensions
+    image_size = ImageSpec.new(file.path)
+    [image_size.width, image_size.height]
+  end
+end

app/logical/media_file/image.rb

@@ -0,0 +1,6 @@
+class MediaFile::Image < MediaFile
+  def dimensions
+    image_size = ImageSpec.new(file.path)
+    [image_size.width, image_size.height]
+  end
+end

app/logical/media_file/ugoira.rb

@@ -0,0 +1,13 @@
+class MediaFile::Ugoira < MediaFile
+  def dimensions
+    tempfile = Tempfile.new
+    folder = Zip::File.new(file.path)
+    folder.first.extract(tempfile.path) { true }
+
+    image_file = MediaFile.open(tempfile)
+    image_file.dimensions
+  ensure
+    image_file.close
+    tempfile.close!
+  end
+end

app/logical/media_file/video.rb

@@ -0,0 +1,9 @@
+class MediaFile::Video < MediaFile
+  def dimensions
+    [video.width, video.height]
+  end
+
+  def video
+    @video ||= FFMPEG::Movie.new(file.path)
+  end
+end