Made it so extension works even if "Show Header" is unchecked

Here's a screenshot of the `Show Header` option.
![screen shot 2014-10-21 at 8 23 55 am](https://cloud.githubusercontent.com/assets/2916945/4718948/89b68eb8-5925-11e4-90ef-78625d667bf7.png)

Since your extension was using that as a litmus test for when to function, it wouldn't hide anything (rewards, gold, gems, etc) if the `Show Header` option was unchecked.

Moving the conditional to a variable allows it to work even if `Show Header` is unchecked.