[Design] next week/previous week keybindings

[Jeffrey Harris]

> Can we use Alt-Arrow for all 3 platforms? 

I don't see why not, but I'd rather not continue ping-ponging
keybindings, so I'll wait to see if anyone has compelling reasons to
choose, oh, I don't know, maybe Ctrl+Shift+Alt+Caps Lock+arrow. :)

Ctrl+arrow navigates words as Davor mentioned, so I moved us to
Ctrl+Alt+arrow, but that conflicted with standard Linux keybindings so
Heikki changed to Ctrl+Shift+arrow but that turns out to mess me up when
I'm editing item titles on Windows.

I'm hopeful that if Alt+arrow is what Firefox binds to navigate history,
it probably doesn't conflict too badly on Mac or Linux, though.

And yes, Davor, that is a level of punning that I can only rise to (or
sink to, depending on your perspective) at the end of the day.

Sincerely,
Jeffrey