implementation of permission mechanism, insight page, refactor

[Rupeshiya]

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Problem

Github Issue Number: #131

1. As of now, only the creators of a particular post/event/project was allowed to perform edit or delete operation, but the admins should also have the access to perform these operations irrespective of the creator.
2. There is no backend for the insight page of the client-side to check the overview of the organisation or members or search any members.l_

Solution of problem

Implemented backend for the above-mentioned problems:
So this PR includes:

1. Backend for fetching org overview
2. Backend for fetching personal overview
3. Get all members info
4. Search member by their names (first name, last name or full name)
5. Added permission check for posts, comments, organizations, User delete backend
6. User logout backend
7. Bugfix in image upload (Organisation part: DB modified)
8. Covered test cases for newly written backend

Type of Change

[✓] Bug fix
[✓] New Feature
[ ] Development of UI/UX prototypes
[✓] Small refactor
[ ] Change in Documentation

Checklist

[✓] My code follows the same style as the codebase
[ ] My Code change requires a change in documentation
[ ] I have updated the Readme accordingly
[✓] I made PR against development branch
[✓] I have run the test cases locally and it's passing.
[✓] I have squashed my commits