Dropdown menus are keyboard navigable

[interim17]

Use Case

First task in making the whole website keyboard navigable, achieve keyboard navigability to W3C standards and set good practices to extend to the rest of the website in addressing accessibility.

Acceptance Criteria

• more visually explicit focus states for focused elements that differs from hover state
• all action buttons keyboard operable
• operable dropdown menus and submenus (w3 guidance on top level menus here)
• navigable/operable modals
• provide name/role/value for interfaces, alt text, aria labels, and aria landmarks, etc where needed

Details

Please provide any helpful specifications

[interim17]

is currently blocked by #575. Need focus states before can test usability of dropdowns