Add SASS support

Hi. Tried to add SASS support (changes in generator: https://github.com/madebysource/generator-pho/pull/6). I have some issue and can't figure out what's going wrong. When i run gulp task it goes just fine but files just don't compile. Also i have problems with configuration file, i moved main style and styles options to index which i guess is unacceptable. Would really appreciate your comments. 
Best regards, 
Pavel