Renamed folder "Models" to "models"

First time using GitHub but I believe I got the forking and pulling right.

It's just a rename of folder, the latest Android Studio seems to complain about the case of the Models folder because it's lower case in code and uppercase on the filesystem.

![models](https://cloud.githubusercontent.com/assets/9936844/5232466/7736e440-7748-11e4-8542-834f2bfaa11a.png)