Integrate the SC.AutoMixin into SC.view, using a new property: autoMixins. Deprecate SC.AutoMixin

This is a followup for issue https://github.com/sproutcore/sproutcore/pull/999

I consider that this auto mixins mechanism should be integrated into SC.View. After the comments done by tyler into the previous issue (#999), we have here an optimized version that should not put any extra pressure on the SC.View.createChildView. The new code is not using any get method because we really don't need them in this context.