Refactored javascript code of admin notification modal popup

[RahulKachhadia]

Description

• Refactored javascript code from popup.phtml according to Magento way.
• Created a JS component file js/system/messages/popup.js

Fixed Issues (if relevant)

1. N/A

Manual testing scenarios

1. N/A

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-cicd2]

All committers have signed the CLA.

[VladimirZaets]

Hi, @rahul-kachhadiya, I took your PR into processing, thank you for collaboration.

[magento-engcom-team]

Hi @rahul-kachhadiya. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.2.5 release.

Please, consider porting this solution across release lines.
You may use Porting tool to port commits automatically.