Use sRGB Color Profile when converting images

With the conversion done when uploading or fetching an image we also
lose any embedded color profiles. [This leads to images possibly not rendered
properly in the browsers.][1] To fix the issue we tell imagemagick to render
the image from the embedded color profile to sRGB, which is the color
space used by most browsers.

RT_sRGB.icm is taken from the [RawTherapee repository][2] and is licensed as Public Domain.

[1]: https://meta.discourse.org/t/image-embedded-color-profile/40519
[2]: https://github.com/Beep6581/RawTherapee/blob/master/rtdata/iccprofiles/output/RT_sRGB.icm

app/models/optimized_image.rb

@@ -108,6 +108,7 @@ class OptimizedImage < ActiveRecord::Base
       -interpolate bicubic
       -unsharp 2x0.5+0.7+0
       -quality 98
+      -profile #{File.join(Rails.root, 'vendor', 'data', 'RT_sRGB.icm')}
       #{to}
     }
   end
@@ -130,6 +131,7 @@ class OptimizedImage < ActiveRecord::Base
       -gravity center
       -background transparent
       -resize #{dimensions}#{!!opts[:force_aspect_ratio] ? "\\!" : "\\>"}
+      -profile #{File.join(Rails.root, 'vendor', 'data', 'RT_sRGB.icm')}
       #{to}
     }
   end