Reader should support galleries preview

[sendhil]

Add Gallery preview to reader like on Android:

Just an FYI: in the Android reader, tapping any image zooms into a view like the one Davide proposes above, and you can swipe through all the images in the post.

[sendhil]

Moving to 4.2.

[sendhil]

Moving to 4.3.

[roundhill]

👍 Just noticed that I missed a few photos from a post because I wasn't shown in the list view that it was a gallery.