Quest image added in the completion screen

referencing https://github.com/HabitRPG/habitrpg/issues/4333, I've added in the image (it wasn't there previously) and made it so that the reward text had to clear the image before starting. This works well because the final text can still float left of the image, but doesn't break it if there is no text. As far as the other issue that was referenced, not all quests have completion text, which is why sometimes no text appears. 
![screenshot 2014-12-11 21 56 22](https://cloud.githubusercontent.com/assets/5234453/5416320/41506626-81e3-11e4-8fc4-6a77c2c63420.png)