Private/rparth07/navigator a11y fix

[rparth07]

Changes:

1. add aria-label to floating navigator button instead of button wrapper
2. add empty alt attribute to button image
3. add aria-label to navigator search button
4. change navigation title from span to h2
5. change navigation sidebar from div to nav and add aria-label to navigation sidebar
6. remove unnecessary css
7. add meaningful specific title attribute to iframe (rather than generic title) to make it more accessible and announced by assistive technologies

Checklist

• [ ] I have run make prettier-write and formatted the code.
• [ ] All commits have Change-Id
• [ ] I have run tests with make check
• [ ] I have issued make run and manually verified that everything looks okay
• [ ] Documentation (manuals or wiki) has been updated or is not required