Relying on this variable may cause issues if the project is incorporated
in a parent project (e.g. when using the current project as a git
submodule).

- Moved all Python scripts in a separate directory
- Generate version file for Python modules
- C++/Python commands are built in "bin" inside the build folder.
- Copy Python scripts in installation directory

On Windows, we need the dlls to be present in the same directory as the command executables.

Users shouldn't have to worry about this/

This is useful for IDEs

Previously, mrview required special handling of QFileOpenEvent and thus bool QApplication::event(QEvent*) was defined mrview.cpp. This strategy is no longer possible since now the code in src is built as a shared library, which requires the function to be defined in the shared library. To get around this we instead rely on a custom event handler using std::function.

Since commands are no longer built in source_dir/bin, we now need to specify the build directory in generate_user_docs.sh