* various minor fixes and cleanups
* support interface{} returns for js/wasm
* fix android builds on darwin
* support for the virtualkeyboard module
* fixes for docker image builds
* cleanup callback handling
* fix possible moc memory leaks
* new virtualkeyboard examples
* js/wasm GOCACHE fix for Go 1.12+
* make use of the official Go 1.12 wasm build and replace js.NewCallback with js.FuncOf
* update docker images to Go 1.12.4
* revive raspberry images
* fix raspberry related bundling issue
* add the multimedia module to the raspberry images
* fix raspberry related QT_API issue
* remove unecessary *char to []byte copy overhead in some unlikely cases
* fix Qt install script
* initial partially support for Felgo (former V-Play) on darwin
* fix charts/audio example and darwin
* fix common/widgets_demo example on iOS (issue #451)
* fix widgets/renderer memory leak
* fix possible QT_PKG_CONFIG + QT_VERSION race condition
* fix static linux docker image