Use Github Actions instead of Travis

Moved MSVC to Github Actions as well.

.ci/linux-mingw/docker.sh

@@ -0,0 +1,25 @@
+#!/bin/bash -ex
+
+# override CI ccache size
+mkdir -p "$HOME/.ccache/"
+echo 'max_size = 3.0G' > "$HOME/.ccache/ccache.conf"
+
+mkdir build && cd build
+cmake .. -G Ninja -DCMAKE_TOOLCHAIN_FILE="$(pwd)/../CMakeModules/MinGWCross.cmake" -DUSE_CCACHE=ON -DCMAKE_BUILD_TYPE=Release -DCOMPILE_WITH_DWARF=OFF
+ninja
+
+ccache -s
+
+echo 'Prepare binaries...'
+cd ..
+mkdir package
+
+QT_PLATFORM_DLL_PATH='/usr/x86_64-w64-mingw32/lib/qt5/plugins/platforms/'
+find build/ -name "threeSD.exe" -exec cp {} 'package' \;
+
+# copy Qt plugins
+mkdir package/platforms
+cp "${QT_PLATFORM_DLL_PATH}/qwindows.dll" package/platforms/
+cp -rv "${QT_PLATFORM_DLL_PATH}/../imageformats/" package/
+
+python3 .ci/linux-mingw/scan_dll.py package/*.exe package/imageformats/*.dll "package/"