[Gssoc'21] Added the 404 page to website with 404 handling code

[arpit456jain]

Related Issuse

There was no 404 page in website

Closes: #152

Describe the changes you've made

https://user-images.githubusercontent.com/55352601/114263991-fae8b200-9a05-11eb-999a-846c817537f2.mp4

Checklist:

• [x] My code follows the style guidelines of this project.
• [x] I have performed a self-review of my own code.
• [x] I have commented my code, particularly in hard-to-understand areas.
• [ ] I have made corresponding changes to the documentation.
• [x] My changes generate no new warnings.

[arpit456jain]

@khannakshat7 I hope In production the debug is false because my code will handle 404 error only and only if debug is false.

kindly review my PR and kindly add the same labels which are on the issue.