html: Fix W3C Validation issues

[pkvach]

Checklist

• All new and existing tests are passing
• I have added an entry to CHANGES.rst because this is a user-facing change or an important bugfix
• I have written proper commit message(s)
  

What changes does this Pull Request introduce?

Fixing following W3C validation issues in HTML:

• Error: Bad value meta for attribute role on element div.
• Warning: Section lacks heading. Consider using h2-h6 elements to add identifying headings to all sections, or else use a div element instead for any cases where no heading is needed.
• Warning: Consider adding a lang attribute to the html start tag to declare the language of this document.
• Warning: The type attribute is unnecessary for JavaScript resources.

Why is this necessary?

Fixes #328