Support opening multiple preset (and playlist) files without requiring an additional command line switch

[kblaschke]

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Currently, projectMSDL only supports the presetPath argument to load presets from a single directory. To make it easier for users to open presets and preset playlists from file browsers or other applications, projectMSDL should support passing in preset files via anonymous arguments which don't require an additional command-line switch like --presetPath / /presetPath.

If multiple files are listed, all of those passed in should be added to the internal playlist instead of using the default preset path/playlist configured.