Update menu to be more accessible

[jasonnrosa]

Types of change

• Bug fix (change which fixes an issue)
• Enhancement (change which improves upon an existing feature)
• New feature (change which adds new functionality)

Description

Updates the menu module to be more accessible (e.g. aria attributes change based on hover/focus, the menu is keyboard accessible without having to tab through every menu item, etc.). This also cleans up the CSS classes used to follow BEM (was previously not closely following BEM) and cleans up code for the module in general to ideally make it simpler/easier to read and use. I generally tried to keep the look of the menu as close as I could to the original with some minor exceptions (e.g flyouts on drop down menus for desktop).

Relevant links

Fixes #286

Checklist

• I have read the CONTRIBUTING document.
• My code follows the style guide requirements.
• I have thoroughly tested my change.

People to notify
CC: @TheWebTech

[jevenson]

I'm seeing this "Show submenu" button visible, when I think its supposed to only be read by a screen reader. Not really sure what the cause is.

[jasonnrosa]

@jevenson great catch - I'm not really positive why that wasn't popping up when testing locally but it looks like it was an issue with the folder name of utilities not matching the include file path in main.css. I was using a helper class on the show for submenu (so it is visible for screenreaders but not visually) but that helper class wasn't getting picked up because of the spelling error in the folder.

[jevenson]

Fix looks good! Thanks!