Fixed icon resolutions

Extension button icons should be 19px or 38px, otherwise the browser performs rescaling which can be suboptimal. For some reason, it's even worse with chrome.browserAction.setIcon than by setting the default icon. I fixed this by creating a correctly rescaled 19px and 38px icon (both from the normal and the apathy icons) and pointing the browser to these. Here's what the difference looks like on my Retina MBP (to the left is the original version):

![screen shot 2013-09-10 at 9 43 15 am](https://f.cloud.github.com/assets/3217744/1112943/3d19e612-19ee-11e3-9aad-5cc33ed258f3.png)
![screen shot 2013-09-10 at 9 43 41 am](https://f.cloud.github.com/assets/3217744/1112944/3d2e95da-19ee-11e3-8341-9cd5be2d0c9a.png)

I believe that even better icons could be created from the original vector art, if you have a few minutes @hsbakshi, you could replace my icons that I created from the 230px versions with Preview.