Add color to calendar events

This feature allows you to optionally add a color to calendar events, for the purpose of tagging (e.g. work events could be one color, social events another). I subclassed UITableViewCell to properly arrange the square of color on the left in table view cells. The CALayer in the color square creation ensures that that square remains visible when table view cells are selected.

![screen shot 2014-06-05 at 1 19 20 pm](https://cloud.githubusercontent.com/assets/5513682/3193084/41344c50-ecee-11e3-86b1-89cfdc1cc3e8.png)