Fix QStringSpinBox Style

.. on Linux and Windows
Fix Overlay Widget

.. easier to grab and resize
.. move when it goes off screen
Fix RideNvigator coloring

.. first one goes invisible
.. hover didn't highlight
Fix Overlay Widget Title Glitch

.. it wasn't centered on the titlebar.
Scrollbar hover highlight

.. on Non-Mac.
Slightly wider scrollbars

.. 4px is too small.
Mac now honours flat theme

.. but not sure its gonna be very popular !
CP Plot Delta as Percent

.. delta plot but with percentage rather than absolute differences

.. particularly useful for plotting PD curve by seasons and looking
   at the gains/losses in percentage terms per season

.. also the differences in short and long durations in absolute terms
   often look quite different, in percentage terms there is often not
   a huge difference over seasons.

NOTE: Needs to be fixed up to do percentage differences by model.
Merge remote-tracking branch 'upstream/master'