Add support for overlapping shifts

### What is the problem / feature ?

Overlapping shifts weren't displaying correctly.

### How did it get fixed / implemented ?

Added a sorting algorithm to sort them onto separate lines in a nice way.

http://cl.ly/image/2J3s2G340K24

### How can someone test / see it ?

Create some overlapping shifts and see that they end up on separate lines.

*Here is a cute baby animal picture for your troubles...*

![2tyl7ag](https://f.cloud.github.com/assets/824194/2435947/923ab8a6-add2-11e3-9ec4-4561fec25cb4.jpg)