Select rarefaction depth

Adds rarefaction depth box at select commands phase of analysis creation
I would say yes to that!

On (Sep-03-14| 9:20), adamrp wrote:
> >          """Builds biom and mapping files needed for analysis
> >  
> > +        Parameters
> > +        ----------
> > +        rarefaction_depth : int, optional
> > +            Defaults to ``None``. If ``None``, do not rarefy. Otherwise, rarefy
> 
> The template uses HTML5 constraints to make sure that the rarefaction depth is a number > 0.  Do we want additional checks in the python code (e.g., to make sure it's not a decimal number)?
> 
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> https://github.com/biocore/qiita/pull/256/files#r17060767