Added database checks

[smarshy]

Added database checks to tests corresponding to CRUD operations in following cases and number of tests-

1. Sign up Admin/volunteer with invalid/valid credentials (16 tests )
2. Create/edit event with valid/invalid details (9 tests)
3. Create/edit job with valid/invalid details (9 tests)
4. Create/edit shift with valid/invalid details (9 tests)
5. Create/edit/delete organization (5 tests )
6. Delete event, job, shift (6 tests)
7. Shift registration, cancel shift registration, edit volunteer profile (5 tests)
8. Add/edit/cancel hours by volunteer/admin (5 tests)

This PR contains the commits from PR #375 as the changes for database checks have been made after the tests were redesigned to follow POM. This was done as otherwise there would be too many merge conflicts to fix.

The actual changes can be seen here once PR #375 is merged or can be currently seen here

[coveralls]

Coverage increased (+4.5%) to 88.229% when pulling ed3cd29 on smarshy:add-db into fd85eb3 on systers:develop.

[tapaswenipathak]

Thank you. ✨