Merge pull request #896 from Joern-R/pull

Translation Enablement + Check on temporary Seasons
RideEditor Cosmetics

.. scrollbars tidied up
.. ugly grid lines removed altogether
Window Style Part 1 of 3

.. refactor linear gradients out of the widgets
   such as toolbar, chartbar, sidebaritem etc

.. GCColor::linearGradient() now returns a gradient
   that is reused across the codebase

.. in Part 2 we will add a colour and flat style
   for the linearGradient

.. in Part 3 we will tidy up the styling for buttons
   and toolbuttons to adopt flat or metal styling too
Window Style Part 2 of 3

.. apply Flat styling across all the widget painting

.. only use WHITE as the flat color for now, in part 3
   we will look at user customisation and updating the
   toolbar and sidebar buttons to also be flat.
Windows Style Part 3 of 3

.. flat colors based upon windows prefrences if on
   windows -- BUT ONLY if Dsmapi.h is available.
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.
Fix tooltip for Compare Delta Percent
Fixup Mac compile on QT < 5

.. blackline doesn't exist compile error.
Translation Enablement

(cherry picked from commit 67be090de9cbc4772147a2ab0b08e28b96d67d12)