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
Merging master
Removing partially added delete code since we are referring its implementation