Add GoogleMaps API to dive site index

https://trello.com/c/BCpf77el/24-create-map

![image](https://cloud.githubusercontent.com/assets/8681076/5129000/db49dee4-70ac-11e4-9df3-1e9b8a2a59a0.png)
map options is a constant, so lets make that clear in the code:

``` js
var MAP_OPTIONS = {
  zoom: 12
}
```

long line is long. Try extracting out the `map_canvas`:
``` js
var createMap = function() {
  // use the jquery selector rather than `getElementById`
  mapCanvas = $("#map_canvas");
  window.map = new google.maps.Map(mapCanvas, MAP_OPTIONS);
}
```