Referential integrity update

[bihanviranga]

Implemented in this commit

• Cannot delete brands if it has tickets.
• Cannot delete categories if it has tickets.
• Cannot delete companies if it has tickets.
• Cannot delete modules if it has tickets.
• Cannot delete products if it has tickets.
• When attempting to delete these entities, if they have tickets, the server will return a 400 status code.

Notes

• SQL script was updated. But the generated dbcontext class was functionally identical to the previous one. So this branch is still using the old dbcontext class.
• Got some issues trying to enforce referential integrity from database engine. Apparently it's a problem that happens when going DB-first. Worked around it by handling it at the code level.
• reference 1
• reference 2

[DhFernando]

well done bokka