Using qwt from https://sourceforge.net/p/qwt/git/ci/qwt-multiaxes/tree/
Applied the following changes to qwt 6.3:
* Added QwtZone to qwt_plot_curve.cpp
* Disabled the emitting of Layout Requests on geometry changes of
QwtScaleWidget - without this, CPU utilization was up to 100% on
one core
Fixes#4495
This commit is based on https://github.com/GoldenCheetah/GoldenCheetah/pull/3956
with the following additions / changes:
* Upgraded to the latest version of the multiaxes-branch, thus eliminating crashes of GoldenCheetah on startup
* Disabled the emitting of Layout Requests on geometry changes of QwtScaleWidget - without this, CPU utilization was up to 100% on one core
* Added the class SplineLookup, reusing small portions of code from Qwt 6.1
* Re-added the splines in WPrime and RideFile (resampling), using the new interface of QwtSpline
* Appveyor: qwt in cache-section now depends on qwt/qwtconfig.prin.in for refresh on version change
