Separate Ctrl-Up/Down from Ctrl-Left/Right...

Separate Ctrl-Up/Down from Ctrl-Left/Right, so they can be enabled independently.

See also http://tabutils.uservoice.com/forums/43097-general/suggestions/2937986-add-possibility-to-change-the-crtl-arrow-shortcut

With this patch, the Left/Right-Setting will retain, but Up/Down must be enabled explicitly.