Add button to go back home from 404.html and add a simple animation

[Mutugiii]

Fixes #40

• Adds a button to go to the home page from the error page
• Adds a simple heartbeat animation to the main subject text of the error page

https://user-images.githubusercontent.com/48474421/162401343-eaf39c6a-47bd-40fa-9e4c-7313419eba52.mp4

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