Gulp fixes

@bartvde this was some work I did trying to fix the watch stuff - it cleans it up a bit to be more 'gulpy' but I don't want to cause any regressions and pain. Mind giving it a spin? I also put rimraf in there
@ischneider workaround removed with https://github.com/MapStory/story-tools/pull/34 let me know if I've misunderstood