#18 Scroll to first event

Adds option to scroll to first event.

Usage:

```javascript
$('#weekly').weekly({
  scrollFirstEvent: 'today'
});
```

or

```javascript
el.weekly('setScrollFirstEvent', 'everyday');
```

**Valid values**:
 - `'today'`
 - `'everyday'`
 - `'2013-12-25'`
 - `new Date(2013, 0, 25)`
 - `false`

If there's no events to scroll to, it defaults to `startTimeScrollOffset` or 8am.