Write vbam.ini to ~/Library/Application Support/vbam on OSX.

Do not create ~/.vbam on OSX in common/ConfigManager.cpp .

Make get_config_path and wxvbamApp::GetConfigurationPath return
directories with a writable parent in reverse search order when no
writable directories in the current search order are available since the
directory is created in OnInit.

This prefers to create the user-local directory and write the vbam.ini
there.