Add numerical entry box for rarefaction depth
Delete hacky code

Fixes #246
Add rarefaction to biom table generation

Right now this is analysis-wide, but some day it should be per-datatype...
Change minimum rarefaction depth to 10
Add sanity checking to rarefaction_depth
Add tests for sanity-checking
Merge pull request #256 from adamrp/select_rarefaction_depth

Select rarefaction depth