Use skbio's alpha diversity metrics
Remove qiime.pycogent_backports.alpha_diversity

You can dance if you want to
Add links to scikit-bio alpha diversity docs

Thanks for suggesting this @ElDeveloper!
replace more observed_species refs to observed_otus
Resolves issue #1398

This issue is incorrectly titled - the G-test error occurs here. In short, this PR removes the abilit to use group_significance.py on a table which is relative abundance.
Resolves forum users concern

Forum posts frequently cite the warning that table has no metadata as an error when using group_significance.py. It actually does not cause failures, just a warning. This clarifies the message.
Missing word.
Merge pull request #1542 from ElBrogrammer/brah-i-alpha-diversity

Remove PyCogent alpha diversity dependency
resolves issue #1316
Resolves issue #1383
Merge pull request #1549 from wdwvt1/issue_1316

Issue 1316 and issue 1383
Merge pull request #1545 from wdwvt1/group_sig_g_test

Group sig g test