move apple-touch-icon-precomposed.png into `images/touch`

as the other touch icons are there.

Reviewer: @addyosmani 

Tested on iOS 8, 7, 6.

![screen shot 2014-08-29 at 14 00 40](https://cloud.githubusercontent.com/assets/170270/4089861/3af6e4d8-2f74-11e4-9c1e-45c1a5a519c0.png)
![screen shot 2014-08-29 at 13 52 54](https://cloud.githubusercontent.com/assets/170270/4089860/3af3567e-2f74-11e4-9df0-2c2d45a268fe.png)
![screen shot 2014-08-29 at 13 52 18](https://cloud.githubusercontent.com/assets/170270/4089862/3b0b0184-2f74-11e4-8ce1-19bf14a49980.png)