Clean up div after component is unmounted

[cuberoot]

Fix web components that are mounted into a container so that they clean up the div that they create.

Description

Remove the div that is created when the web component in unmounted

Related Issue

#11

Motivation and Context

I have a case where I am mounting/unmounting a component (popover) and the divs are piling up.

How Has This Been Tested?

See the test that I added in the PR to detect this. It fails without my change to WebComponent

Types of changes

• [x ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x ] I have signed the Adobe Open Source CLA.
• [ x] My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• [x ] I have read the CONTRIBUTING document.
• [x ] I have added tests to cover my changes.
• [x ] All new and existing tests passed.

[alexmirea]

Thanks for the contribution @cuberoot