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

Separate Ctrl-Up/Down from Ctrl-Left/Right, so they can be enabled independently.

This patch introduces a new preference called extensions.tabutils.handleCtrlArrowUpDown which will be used for Ctrl-Up/Down exclusivly.

See also http://tabutils.uservoice.com/forums/43097-general/suggestions/2937986-add-possibility-to-change-the-crtl-arrow-shortcut for reference.