Qt 5.6 support for lowend platfroms (arm, mips)

[shrkamat]

This is preliminary attempt to support Qt 5.6 on low end platforms.

1. Strip Quick.Components, wdigets, svg to reduce memory.
2. Application would have to spawn QGuiApplication and not QApplication.

TODO:

Add compile time config to spawn QApplication / QGuiApplication
Move QtQuick Controls classes to a different go package (like QQuickStyle, currently deleted)

It will be great if I am guided a bit on the TODO(s)

[nanu-c]

This looks somhow limited and shouldn't remove the support for qqc2. And why are you using a qt version that isn't supported anymore since 3 years? Also in the more recent version have undergone a huge performance rework so i think it's better to use a newer version.