Revert "Merge pull request #62 from squirrelo/cascade"

This reverts commit f5df8bbb94eec58451bda990aa57098b342fceb4, reversing
changes made to f880690a6d4cbce878c45d87e8e5b7d75c3defc1.
Merge pull request #63 from josenavas/revert-pull-request-62

Revert "Merge pull request #62 from squirrelo/cascade"
Changing staticmethods to classmethods
Adding exists classmethod to the base class
Merge pull request #64 from josenavas/exists

Add exists classmethod
More db changes
add investigation object skeleton
Add eq and ne checks for user
added equality check to base class
change _table name
change sample_id to varchar
Merge pull request #66 from squirrelo/skeletons

Skeletons
fix base eq check and add data skeleton
Remove extra check
Merge branch 'master' of github.com:biocore/qiita into moredb
Merge pull request #65 from squirrelo/moredb

More db changes
populate study_preprocessed_data table for tests
Merge pull request #68 from squirrelo/testdata

populate study_preprocessed_data table for tests
break up if into two statements
test base eq ne