Collateral class added.

[Purvanshsingh]

I have added Collateral class to NPL Vocab & ApiDoc.
All the CRUD functionalities are added to the Collateral class.

DB structure with Collateral class :

GET, PUT, & POST operations :

[open-risk]

Some further tests:

• To test with actual loan id's
• To test multiple collateral with same loan id
• To test cascaded delete of collateral if the borrower class to which loan (and collateral) is linked is deleted

[Purvanshsingh]

@open-risk I have added the mock_portfolio_generator.py script.

It generates :

• 100 borrowers with no loan & no collateral
• 100 borrowers with loan & no collateral
• 100 borrowers with loan & collateral

And add them to the database via PUT request.

Borrower -> Loan -> Collateral are linked with the foreign key.

Tested: on deleting a borrower the respective Loan and the collateral associated with the loan_id deleted automatically.