Add custom validation to form

[Amnish04]

I have added custom validation features to the input elements.

The Generate Card button gets dynamically enabled only if:

1. All the properties marked as required have been entered.
2. At least one of the social media link has been entered and is of correct format.
3. All the input elements are in valid state.

Please review my changes, and let me know if something needs to be changed.

This closes #47

Update: I just added * symbol before labels for every required field.

[piyushkdas0611]

Thank you for contributing, do star repo

[Amnish04]

@piyushkdas0611 You're welcome. Just one thing, could you please add hacktoberfest-accepted label to the PR as well? For some reason, its not counting towards my progress.

Thanks in advance!