Fix Ctrl+PageUp/PageDown keyboard shortcuts
This got broken in 3b58e4a9 when multiple shortcut sequences were added to a single QKeySequence object, rather than a list with multiple QKeySequences in it. As a result, the single QKeySequence object discarded all sequences after the first, so the Ctrl+PageUp/PageDown shortcuts got discarded.
There may be other instances of this error, but this was just the one I noticed and need urgently fixed to avoid throwing the computer out the window. :)