Add head request to base handler

As seen with american gut, we need to respond properly to HEAD requests. This adds that functionality.
@squirrelo, does that mean that this method needs to be added somewhere
else? Or by adding it to BaseHandler we are good?

On (Oct-23-14| 7:31), josenavas wrote:
> > @@ -28,6 +28,10 @@ def write_error(self, status_code, **kwargs):
> >                          request_info=request_info,
> >                          user=self.current_user)
> >  
> > +    def head(self):
> > +        """Adds proper resonse for head requests"""
> 
> `resonse -> response`
> 
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> https://github.com/biocore/qiita/pull/495/files#r19280539