Movie + InTheaters: Retina devices fix.

These fix does three things:
- is_retina is now deprecated so we're switching to DDG.is3x and DDG.is2x.
- Using is_retina fails on IE 10 and lower. Turns out undefined variables are invalid, but window.is_retina is valid.
- The posters are blurry on iPhone 6 Plus (3x screens) so we use the original image.

#### Old:
![xkmadhu](https://cloud.githubusercontent.com/assets/81969/4883843/38f0f298-6366-11e4-9b12-170d02c9fb3e.jpg)

#### New:
![evvkbrx](https://cloud.githubusercontent.com/assets/81969/4883844/38f203e0-6366-11e4-9386-c41f16a70fb8.jpg)