[TOC] Write UI Tests and dev components page

[gabrielwalt]

• Don’t allow authors to configure invalid options in the dialog by validating the options and preventing a start level that is bigger than the stop level.
• Don’t throw errors on invalid configurations, but rather warnings as errors might be monitored and escalated.
• Order both the start-level and the end-level drop-downs the same way (ascending, from H1 to H6).
• Rename the title levels to "H1"-"H6" in the UI and to h1-h6 in the JCR persistence and in the JSON returned by the Sling Models.
• For titles that have the same text, make their ID unique by appending a number, but don’t append anything to titles that already are unique.
• Keep up the amazing work, we're almost done!

PR - https://github.com/adobe/aem-core-wcm-components/pull/2030 

[gabrielwalt]

@adobe export issue to Jira project SITES

[github-jira-sync-bot]

:white_check_mark: Jira issue SITES-2580 is successfully created for this GitHub issue.