Feature request: Add single key shortcut for Reader View

[blackketter]

The default key shortcut for "Show Reader View" is shift-command-R. I think this is a common enough action that a single key to trigger reader view would be great. R is taken for "mark read", so maybe "V"?

[blackketter]

I'd like to amend this to suggest other single key shortcuts be added, including:

• 1, 2 and 3 for Today, All Unready, and Starred (already command-1, 2, 3 respectively)
• ' for Clean Up (already command-')

Ideally, this would be in conjunction with #508 to be customizable.