Fix building and testing on AppVeyor
Fix building and testing on AppVeyor

The default AppVeyor build worker image, Visual Studio 2015, doesn't
contain Qt 5.3 nor Boost 1.59.0 anymore.

See https://www.appveyor.com/docs/build-environment/#boost and
https://www.appveyor.com/docs/build-environment/#qt.

AbletonAG/aqt-stylesheets,AbletonAG/aqt-stylesheets