[Build] Port whole project to CMake build system

[Wohlstand]

Port everything to CMake and completely drop support for QMake build system

Why

• Current build system is overfilled with clunky workarounds and not friendly for developers
• QMake's functionality lacks lot of features are can be useful especially for libraries and hardware-dependent things
• Because of QMake's functionality, lot of things are done in BASH/BAT scripts
• The complete existing build system is hard to maintain

To do

• Basic build
• Dependencies bootstrapping
• Improve library linking interface thing
• Linux deployment
• macOS deployment
• Windows deployment
• Optimize libraries linking process
• [ ] Allow dependencies to be built as shared libraries to allow easier hot-swap of them while developing some things (This item was moved to here: Add ability to compile set of shared libraries AudioCodecs#5)
• Implement lupdate from the CMake directly without of relying on old QMake projects
• Change the build instruction to fit new CMake build system. Put old build guide into the separated page
• Remove old build system. In the guide mark the last commit that still use legacy build system and refer the "Old build manual" article.

[Wohlstand]

One note to optimize the library linking:

Instaed of using things like this:

list(APPEND PGE_MUSPLAY_LINK_LIBS
    ${SDL_MIXER_X_LIB}
    FLAC$<$<CONFIG:Debug>:d>
    opusfile$<$<CONFIG:Debug>:d>
    opus$<$<CONFIG:Debug>:d>
    vorbisfile$<$<CONFIG:Debug>:d>
    vorbis$<$<CONFIG:Debug>:d>
    ogg$<$<CONFIG:Debug>:d>
    mad$<$<CONFIG:Debug>:d>
    id3tag$<$<CONFIG:Debug>:d>
    modplug$<$<CONFIG:Debug>:d>
    ADLMIDI$<$<CONFIG:Debug>:d>
    OPNMIDI$<$<CONFIG:Debug>:d>
    timidity$<$<CONFIG:Debug>:d>
    gme$<$<CONFIG:Debug>:d>
    zlib$<$<CONFIG:Debug>:d>
)

Is a much better way to link dependencies (already used in libADLMIDI and libOPNMIDI projects, as example):

add_library(ADLMIDI_IF INTERFACE)
if(libADLMIDI_SHARED)
    target_link_libraries(ADLMIDI_IF INTERFACE ADLMIDI_shared)
else()
    target_link_libraries(ADLMIDI_IF INTERFACE ADLMIDI_static)
endif()

# ...

target_link_libraries(adlmidiplay ADLMIDI_IF ${SDL2_LIBRARY})

[Wohlstand]

Windows deployment note

As Windows builds are still rely on shared libraries, is need to use WinDeployQt tool to pull all dependent libraries. To easier make this, it's an example function made in another project:

https://github.com/equalsraf/neovim-qt/blob/master/cmake/WinDeployQt.cmake

[Wohlstand]

https://ci.appveyor.com/project/Wohlstand/pge-project/build/0.4.0.3.1303 First Windows build completely deployed through the CMake run.

The only left a macOS deployment to be ready to completely drop away the old building system.

[Wohlstand]

Since recent moment, QMake build support has been completely removed.

[Wohlstand]

Okay, looks like the whole CMake based system is works fine, so, I'll close this.
Any future CMake build related works will be done in separated tasks.