Keyboard support: Board view

[chenilim]

Keyboard navigation is needed in general. This issue tracks the need to be able to use the board view / editor with just a keyboard. E.g.

• Activate viewHeader actions (sort, filter, etc.)
• Select card
• Open card
• Etc.

More complex actions:

• Select multiple cards (shift+arrow)
• Move card(s) to different columns
• Etc.