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
Upgrade to QWT 6.0.1, but still uses a locally patched copy
since support for 8 axes has not been included, despite it
being a relatively simple patch.
Fixes#634.
Fixes#567.
