[Gssoc'21] Added the dark mode with toggle button

[arpit456jain]

INCLUDE ALL NECESSARY FIELDS AND DELETE FIELDS THAT ARE NOT NECESSARY.

Description

Include a summary of the change and relevant motivation/context. List any dependencies that are required for this change.

https://user-images.githubusercontent.com/55352601/114260828-c28ca800-99f4-11eb-8b1e-ec624b85f562.mp4

Fixes #75

Type of Change:

Delete irrelevant options.

• Code
• Quality Assurance
• User Interface

Code/Quality Assurance Only

• New feature (non-breaking change which adds functionality pre-approved by mentors)

How Has This Been Tested?

Uploaded a video above

[arpit456jain]

@rupeshmohanty kindly review my PR

[arpit456jain]

https://user-images.githubusercontent.com/55352601/114261238-1bf5d680-99f7-11eb-8691-e99453fbb16c.mp4

I just notice that find project partner button was not working in dark mode so i had fixed it.

[arpit456jain]

@sakshi300699 @ishubham21 kindly review my PR

[arpit456jain]

@ishubham21 actually there is a img on main page (index.php) I can't change its color so i had added a on it just like a black layer . If you want I will remove it no issues. and I will try to make color contrast better

[arpit456jain]

https://user-images.githubusercontent.com/55352601/114270551-a0158180-9a2a-11eb-907d-4e4a0db6349d.mp4

@ishubham21 check now

[arpit456jain]

Thanks @ishubham21 . @sakshi300699 @anika-001 kindly review my PR

[arpit456jain]

Thanks @anika-001

@rupeshmohanty kindly review it