Use the new Qt5 plugin architecture

Q_EXPORT_PLUGIN2 deprecated. Replaced by Q_PLUGIN_METADATA
Find the Qt5 RCC executable to generate qrc_* files.

Change-Id: I86e6664e85015e3817d80d5dad1b04deeffe1459
Updated QtTesting to use Qt5

QtTesting should use user selected Qt version
Change-Id: I22337268e9864b5fe2153309f6844cdf3ab4e4b3
Import Qt5Widgets module at the top level

This ensures all the required Qt5 variables can be found.
For example, just importing Qt5Core does not help find QT_UIC_EXECUTABLE using
the macro "get_target_property(QT_UIC_EXECUTABLE Qt5::uic LOCATION)". This must
be a Qt5 bug.

Change-Id: Ie6f4a708682ad8cf2391d218c193d8127e4c44f7