The Windows dependencies need downloading before Eigen is configured

Refs #0

Also got rid of the brittle inspection of the architecture
and distribution favoring `CPACK_RPM_PACKAGE_RELEASE_DIST`
introduced in cmake 3.6.

https://cmake.org/cmake/help/v3.6/module/CPackRPM.html

Refs #0

This also removes support for packaging trusty (14.04)

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Required for mslice and will be required for
the workbench in the future

Refs #21679

QWebEngine replaces QWebKit in Qt>=5.5.
Refs #20381

Refs #20381

The Qt4/Qt5 plugins cannot be loaded into the same process so
need to be separated at build time.
Refs #20288

Along with disabling environment variable updates by default.
Developers will not then accidentally build a release package
when building locally.

Refs #20288

Refs #20288

Refs #20288

Refs #20288

This paves the way for using QWT6 in an external project in the future.
Refs #20288

Refs #20288

It now produces import targets rather than relying on finder variables
Refs #20288

Refs #20288

Refs #20288