NowNext methods in Bamboo

Added isOnNow and isOnNext methods to the Broadcast model in Bamboo + tests
Not sure this will always work, probably better to use http://uk3.php.net/manual/en/datetime.gettimestamp.php.

```php
$nowTime= new \DateTime('UTC');
$startTime= new \DateTime($this->getStartTime());
return $startTime->getTimestamp() > $nowTime->getTimestamp();
```

Probably work?