Don't relayout text on media update if the media frame does not change.

Also improves frame size calculation.
Refs #149
Reader: Load reader detail images and refresh in batches.

Refs #149.
Merge pull request #347 from wordpress-mobile/issues/149

Performance improvements for loading images in reader detail.
Don't relayout text on media update if the media frame does not change.
Reader: Load reader detail images and refresh in batches
#149