Updates and fixes for Beat Saber 1.39.0

[qqrz997]

• Added reference to BeatSaber.BeatmapEditor for 1.39.0
• Added InstalledMods - this centralizes all checks to see if certain soft dependencies are installed
• Now checks to see if BeatSaberPlaylistsLib is installed before trying to access any of its types, and will continue to work fine while BeatSaberPlaylistsLib is not installed. All references to BeatSaberPlaylistsLib are now in PlaylistSongUtils which reduces the amount of complex logic from the calling end
• Fixes the video menu not being reinitialized on internal restart by resetting the VideoMenu.Instance - this is more in-line with game logic since the menu should not persist through internal restart

_{P.S. remember to bump the manifest mod version before uploading to BM}