[Lens] Formula Docs Design Update

[MichaelMarcialis]

This PR should addresses some small design issues I found while reviewing @flash1293's earlier documentation PR, which has since been merged. Design issues addressed include:

• Correcting CSS border issues on formula editor interface when documentation is collapsed in full screen mode.
• Refactoring the documentation navigation and text markup to be more semantic.
• Improving the hierarchy of the documentation navigation.
• Refactoring the documentation object structure to better covey the parent/child relationship.

Let me know if you have any questions. Otherwise, feel free to merge.