Removed default folder icons (as per #16)

Sublime Text 3, build 3065 for me, has the default folder icons next to the custom Flatron ones (see below).
![screenshot 2014-10-07 11 22 50](https://cloud.githubusercontent.com/assets/2782749/4544776/ea2494f2-4e35-11e4-8160-288457e19f94.png)

This addition removes it, yielding the following result:
![screenshot 2014-10-07 10 37 23](https://cloud.githubusercontent.com/assets/2782749/4544629/d8cb9f4e-4e34-11e4-8e7d-3f2ae91b6860.png)