.. 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.
.. 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
.. now has an overlay widget that can contain multiple widgets
and is user movable and resizable etc
.. we show the model derived values for now, but could add other
things at a later date (e.g. MU distribution etc).
Fixes#811.
