Piper/shifts that span midnight

### What is the problem / feature ?

Shifts that span midnight were not supported by the interface. They would only show up on their starting date, and they would not respect the maximum number of columns in the table.

### How did it get fixed / implemented ?

Shifts now appear on all days that they intersect.  The Javascript was also updated to update all instances of a shift on the page when you claim a shift.

@Zaskoda there are two new classes that need styling.  `cutoff-left` and `cutoff-right` for shifts that extend beyond the day boundry.  These should probably be styled to not have a round border on the left/right side of the cell.

### How can someone test / see it ?

Make a shift that overlaps with midnight and see that it is rendered correctly.

*Here is a cute baby animal picture for your troubles...*

![il_fullxfull 186131560](https://cloud.githubusercontent.com/assets/824194/2537690/2c9a6b7e-b5b4-11e3-8950-02af2eb8f102.jpg)