status: add up/down keyboard shortcuts

Signed-off-by: David Aguilar <davvid@gmail.com>
status: remove magic number

Signed-off-by: David Aguilar <davvid@gmail.com>
status: remember selection across updates

Teach the status widget to properly restore the selection across
updates.  This ensures that multiple selected items stay selected across
refresh operations, e.g. Ctrl+R refresh or updates from inotify.

Closes #165

Reported-by: @futureweb via github.com
Signed-off-by: David Aguilar <davvid@gmail.com>
inotify: lessen the update interval

There's no downside to waiting just a little bit longer before
triggering update events.  This also helps to lessen the impact of
inotify floods.

Related-to: #165

Signed-off-by: David Aguilar <davvid@gmail.com>