Replaced screenshot writing with Imagelib for pxmv

[APAmk2]

This PR also adds alpha-channel for screenshots, means that you getting screenshot with model only now.
Example:

[SNMetamorph]

It does not compiles on Linux:

FAILED: Debug/primext/devkit/pxmv 
: && /usr/bin/c++ -g -Wl,--dependency-file=utils/pxmv/CMakeFiles/pxmv.dir/link.d utils/pxmv/CMakeFiles/pxmv.dir/__/__/game_shared/bone_setup.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/__/__/game_shared/ikcontext.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/__/__/game_shared/jigglebones.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/__/__/game_shared/mathlib.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/__/__/game_shared/matrix.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/__/__/game_shared/procbones.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/__/__/game_shared/stringlib.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/__/common/conprint.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/__/common/file_system.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/__/common/cmdlib.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/__/common/zone.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/__/__/public/crclib.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/ControlPanel.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/FileAssociation.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/GlWindow.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/ViewerSettings.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/mdlviewer.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/pakviewer.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/studio_render.cpp.o utils/pxmv/CMakeFiles/pxmv.dir/studio_utils.cpp.o -o Debug/primext/devkit/pxmv  utils/mxtk/libmxtk.a  utils/imagelib/libimagelib.a  vcpkg_installed/x64-linux/debug/lib/libfmtd.a  /usr/lib/x86_64-linux-gnu/libQt5OpenGL.so.5.15.13  /usr/lib/x86_64-linux-gnu/libQt5Widgets.so.5.15.13  /usr/lib/x86_64-linux-gnu/libQt5Gui.so.5.15.13  /usr/lib/x86_64-linux-gnu/libQt5Core.so.5.15.13  -lGL  utils/squish/libsquish.a  vcpkg_installed/x64-linux/debug/lib/libminiz.a && :
/usr/bin/ld: utils/pxmv/CMakeFiles/pxmv.dir/ControlPanel.cpp.o: in function `ControlPanel::handleEvent(mxEvent*)':
/home/runner/work/PrimeXT/PrimeXT/utils/pxmv/ControlPanel.cpp:744:(.text+0x47f1): undefined reference to `mxGetSaveFileName'
/usr/bin/ld: /home/runner/work/PrimeXT/PrimeXT/utils/pxmv/ControlPanel.cpp:821:(.text+0x4d7c): undefined reference to `mxGetSaveFileName'
/usr/bin/ld: utils/pxmv/CMakeFiles/pxmv.dir/mdlviewer.cpp.o: in function `MDLViewer::handleEvent(mxEvent*)':
/home/runner/work/PrimeXT/PrimeXT/utils/pxmv/mdlviewer.cpp:413:(.text+0x1856): undefined reference to `mxGetSaveFileName'
/usr/bin/ld: /home/runner/work/PrimeXT/PrimeXT/utils/pxmv/mdlviewer.cpp:592:(.text+0x21a0): undefined reference to `mxGetSaveFileName'
/usr/bin/ld: utils/pxmv/CMakeFiles/pxmv.dir/pakviewer.cpp.o: in function `PAKViewer::OnExtract()':
/home/runner/work/PrimeXT/PrimeXT/utils/pxmv/pakviewer.cpp:431:(.text+0x1149): undefined reference to `mxGetSaveFileName'
/usr/bin/ld: utils/pxmv/CMakeFiles/pxmv.dir/studio_utils.cpp.o:/home/runner/work/PrimeXT/PrimeXT/utils/pxmv/studio_utils.cpp:245: more undefined references to `mxGetSaveFileName' follow
collect2: error: ld returned 1 exit status