Keyboard navigation

[lmorchard]

Ensure keyboard navigation in the popup is supported

[sevaan]

From Issue #63:

Keyboard navigation possible improvements (probably needs a separate issue). Initial focus is correct - the whole panel is focused. Consequent focus should go to the list of possible snooze options. And after that to the bottom menu bar. Next TAB should blur the panel completely and go to the next widget in the browser. I would suggest the following interactions:

• Current active element should always be visible to the user.
• When the panel has a list of options or a list of snoozed tabs user should navigate the list with up and down arrows and the focus should be maintained on the list container. Pressing enter should do the same things as clicking on the list item. (when on the manage panel, this will help with automatically showing delete button when list item is selected with a keyboard). Delete should have a keyboard shortcut when delete button is pressed.
• Calendar widget should maintain keyboard focus on grid container and internal navigation (within the grid) should happen via arrow keys.

[lmorchard]

Kicking out of a milestone for now