Standardizing documentation

[mortonjt]

May want to consider correcting/standardizing of the code documentation. For instance in qiita_db/metadata_template/base_metadata_template.py there are some methods with DataFrame in the Parameters section that should actually be pd.DataFrame

[ElDeveloper]

Related to #321, is there any way to programmatically check that we are doing this right? IIRC the answer is no.