Implementing input validation for contact form

[centurion6x]

Related Issue

Input validation on the contact form

Closes: #102

Are you creating this PR under Hacktoberfest

Yes, I'm opening this PR under hacktoberfest.

Describe the changes you've made

contact.html

Added the necessary elements to display error messages and hidden label elements to carry the names of the fields.

style.css

Added some styling to display the new elements conditionally(position, color, visibility etc.)

validator.js

The validation logic is implemented inside the validator class. This allows for easier implementation of more forms and any input field in the future.

Describe if there is any unusual behaviour of your code(Write NA if there isn't)

NA

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.

Screenshots

[yashikabhargava]

@centurion6x Great work, Thank you for contributing :)

[centurion6x]

Thank you for being an awesome maintainer! love contributing to this project :heart:

[yashikabhargava]

@centurion6x Thank you, it means a lot : )