Add checked-in coaches to homepage

* Added jQuery, because come on now
* Create a [Firebase](https://www.firebase.com) connection to pull coaches that have "checked-in" to DBC
* For each checked in coach, append a link to email them under a new header in the nav bar

![Screen Shot](https://cloud.githubusercontent.com/assets/2602872/4893454/38cab5d6-63c2-11e4-829b-e0f56fc092f5.png)